Once in a while you can ho there with your kids for a fun time picnic. This is, I believe, the least crowded of the historical monuments in and around Delhi.
The fort is in bad shape for now and some parts have broken too. But you can take a lot of cool pictures with your kids and can understand the importance it holds in Indian History.
Some people also like to go for a small peddle boat ride in a small pond in there, but personally I'd rather avoid that. We visited there in the rainy season and it seemed all covered with Moss patches. Some kids may want to put their hands in the water which can be extremely risky. You do not want to manage fidgety kids in the middle of the pond on a peddle boat.
The place also, at certain points, smells like p**. Be careful around that area and rather move on from there.
There are lots of trees and we'll, my boys went climbing on them..while others enjoyed snacks we were carrying.