National Arboretum, if you have a car and esp. if you live in Northeast. Buildings are closed but the park is huge and always has very few people. Lots of room to run and play in the main picnic area/field. old columns from the capitol fun to explore. some of the gardens have probably started blooming too, although that's less interesting for kids.

Hi OP,
I have 8 year old twin boys and we live in an apartment. It's hard to contain them in the morning. But this is our schedule: we study a bit in the AM, they also go on their ipad, and then every day between lunch and dinner we go out for 2-3 hours to trails, walks and they play soccer in the park. WE would go crazy if we don't do this. Ideally, we should go out both in the AM and PM I think.

We are getting outdoor time first thing in the AM. Wake up, eat breakfast, go out and walk for a spell. Then come home and shower and start working. Then go out again in the later afternoon/evening

I will say that this is much easier with an older elementary child than it would be with younger children.

NP - take a scooter to any open path or take some chalk for a starting line and have them run races. My 2 year old scooters, runs down hills and loves to kick balls. Go to any of the parks with a creek or run and let them splash and throw rocks. I would go to any of the paved paths around the Mall or monuments. on the VA side (near Gravelly point) or to glen echo/Georgetown area. Or find a church and use the parking lot. Take bubbles one day. I take my kids out first thing every morning for 2 hours. When we get home, they do their a schoolwork and then amuse themselves. If we take them outside for an extended period first, it’s much easier to get anything g done. That said, it is also much easier bc we have 3, so they all run around together and entertain each other; this is the only time I have ever felt bad for parents of only children.