We're in a flat with no garden or balcony, with toddler DD. We go for a long walk every morning, which really helps. Lots of parks and open spaces within walking distance, I've actually enjoyed exploring different places that we've never been to before, like small garden squares and churchyards. DD probably spends more time outdoors than she would have pre-lockdown (we used to do lots of indoor activities like stay and play, and music/swimming classes).
Today we went to a big local park which was policed by volunteers with megaphones. I found the atmosphere really oppressive, although there was no criticism directed at us. They sealed off all the benches and were telling off people who were doing exercises on the grass (burpees and pushups). We were moving most of the time, but DD wanted to stop and look at the ducks/squirrels (like we would on a normal walk) and I was worried I'd be told off for doing that.There are smaller parks near us which are barely policed at all, yet everyone manages to stay socially distanced and use the space sensibly (including sitting for a rest after exercise, and a snack). I find these smaller places a much more pleasant place to be. I think churchyards are particularly good because they tend to be looked after by the church, so the council has a bit less input into how the rules are interpreted.
I do sit down with DD sometimes when we go out, but mainly because she likes climbing on benches and walls and sitting down, and sometimes to sit down and let her have a snack. I've not had any problems with doing that, but it's been in quieter green spaces, where there isn't any policing (most of the time it's practically deserted).
DD loves water play but I just let her have a long bathtime and play in there, rather than risk getting water everywhere.