So, where were we?
Right, architectural solutions, by sense.
Taste and Smell.
I'll start with Smell. It's funny that we tend to ignore this one, when it is so profoundly cross-wired into our psyches. I just read an article by a woman who lost her sense of smell, and ... well, it's a huge loss. It affects all sorts of layers of joy and happiness. Depression is a huge problem. Memory, nostalgia, our sense of place all tie into the sense of smell. Enrichment is not, however, the same as putting up candles and incense and airwick all over the place. The point of enrichment is meaningful scent. One aspect of this is cooking - not just heating up, but cooking, which fills the entire enclosed area with the aroma of the meal to come.
Another aspect of this is open windows, when this is at all possible, or otherwise experiencing the scent of the earth. Dirt, gardening, walks in parks, growing an herb garden on the windowsill or in window boxes, flowers, trees, water (fountains, pools, oceans, creeks, even marshland)... the experience of nature is embedded with scent. Enrichment with scent also includes learning to identify the herbs and spices of our foods by scent, and to find and use scents for comfort (lavender under the pillow, say). Identifying flowers in bloom by scent is a joyful game for many small children. What is it? Close your eyes, smell, and guess.
And then there's impoverishment, again. This is found perhaps in the reduction in the constant barrage of scents. Urban living is full of odors, often changing rapidly as we move along (granted, we're small-town-ish, not urban, but it still happens). Slowing down and noting the transitions of the smells, both good and bad, is one way to control and contain the information flow. Finding a place that has one strong steady smell, like a beach, can also be useful. The scents tend to drop to the background when they're constant. But the information is still there.
And now taste. Taste has some complex issues when it comes to toddlers. They're not really interested in exploring flavor once they hit about 2, at least where it comes to food. A few will remain interested in variety, but more will want to have the same same same all the time. This is genetic, and it probably relates to survival - toddlers and preschoolers able to leave mom's side would be more at risk if they ate everything they touched. So fearing new foods is a very helpful adaptation. The tastes will come back, in time, for most of them. Trying to force foods is just going to cause fights, though.
Instead, it may make more sense to explore taste without food. Herb gardens are one way. There's way less social/emotional/family pressure around, say, tasting a plant, than tasting grandma's cooked carrots. Growing a vegetable garden is another way for the kids to explore taste - trying, seeing if it is good, is far more fun if you grew it. It still might not be good, but it may be interesting.
And while it might not be the ideal approach, things like pet feed and bird seed can be fascinating explorations of taste. For the most part, cat and dog food (dry, presumably) won't cause any harm if nibbled (watch for choking hazards). Making food for the birds, and seeing if we like it, too, is another thing to explore (use appropriate caution with peanut butter). Other ideas: Making home-made play-do, that can be tasted, good. Tasting snow (fresh caught, LOL!), making ice cream, asking your child for advice on what else to put into the sauce ('can you sniff these herbs, and taste this sauce and tell me what you think I should add?' - my mom played that with me quite often, and I loved it as a game.)
Many people my age were raised with a horror of eating things that might be dirty - the extremes of sterilize/clean were impressed on us. But the hygiene hypothesis suggests that there's such a thing as too clean, too sterile, and it isn't good for us. Tasting a rock to see if they taste like anything maybe isn't a bad idea. Maybe not one from the sludge, though. Apply reason, not horror.
So, that's the major senses, other than sense of self.
What, though, if your child resists any attempt to prune or enhance? How do you deal with the concept of ownership of toys or books, at the same time as dealing with impoverishing the environment? How does one get past the natural tendency of the 2 1/2 - 4 1/2 (er, 6 1/2?) year old to HOARD ALL CHERISHED THINGS?
What we did was to give total power to return the item to circulation. At first, when we instituted the toy library, there was a lot of stressful running up and down, bringing items back out. We did the one-for-one trade option (though there was always creep anyway). We gradually moved toys into the 'to go down' box, and they fished through those as we picked it up to take it away to be sorted back into the bins. But as we kept allowing them to go get that one thing, they eased up. The toy library became their space, not 'invisible space'. They still tend to tear through it like a tornado, but if I say to them, 'I'm going to clear things down to the library - what two classifications of item do you want to keep?' they will think quite clearly about what it is they're playing with most, and wave a hand as they turn back to their work, and say, 'the rest can go down' with nary a blink.
It becomes a matter of choice. But it has to be brought in gently, unless you've started with it from the beginning, because it can easily smell a lot like parental control. I know people who use the library concept, but have the shelves nearer the play area. Some kids find that too distracting, though, and cannot enjoy the space and the play without wondering what's in THAT box, and the other, and what about this one? A separate room, accessible, is good. Harder in apartments, I know. Our house is tiny, but not quite apartment size.
Limiting what comes in to only that which is loved, beautiful, and quality is another way to go. But working that from the gift angle is hard, and so much cheap plastic crap (CPC, I think that term is from Moxie) leaks in around the edges. Add in loving grandparents, and the tide of even quality items can overwhelm. And if we had any issues of deprivation or want or envy that weren't handled well by our parents or peers ourselves, it becomes even harder to stem the tide - we don't really want to stop it, or are conflicted. Certainly I'm guilty of this with books. I could never have enough books as a kid. Now, my kids have effectively, too many. We could fill a small-town school library, with everything from science to literature, fiction, poetry... books. Love books. Too many books and one can't take care of them. More than 75% of the shelf jammed with books and to a child it looks like there's no place to put any more back.
And ownership - Since I had items taken away and sold without my permission as a child (and I remember it), I'm touchy about giving a child a gift and then treating the item as if it did not belong to the child at all, but to the adults. If you give it to the child, it belongs to the child. The toy library shouldn't be a taking away so much as a home for things not being used right this moment.
There are sensitive periods for the concept of organization and order. Preschool is one of them, but the earlier, the better. Once you get toward 4 or so, order itself transitions to organizing/categorizing (at least in my kids), and the emotional hoarding is a big deal, so having many places to put things (safely, in special places) is more important than having few or many items to start with. The next sensitive period seems to be the highly DISorganized 7-year-old stage, when their minds are transitioning from logic to social processing again, and they can again be coached and guided through the problem-solving, gently but frequently, with an assumption that it will take a good solid year for any of it to really develop as a strength of skill (remembering that one is dealing with a brain that is in flux in major ways). It is much easier to get them to choose what to keep out or put away when they get closer to 7. This doesn't mean don't try between now and then, but don't panic and tread gently when/if they resist. It's normal for them to cling to things at that age. And instead, find other impoverished spaces for them to inhabit - something as simple as a basketball court can be a blessing.
A lot of the process of architectural solutions is found in the intersection of their developmental level (as Cathy noted earlier) - the same issues of boundary and exploration will come up again, with a new spin and flavor depending on the age, over and over. That's why I often talk about parenting as a garden, with seasons, and years and years of season after season in which to work. Toddlerhood is just one of the seasons.