Impossible? No. Highly improbable? Hell yeah. What are the odds that they're wearing the same clothes, same haircuts, and playing in the exact same spot and the exact same way as when he left?

And even though they didn't indicate how much time had passed, those kids are young enough that they should have physically changed in some way even if it was only months later. Though I find it unlikely it had only been months. Cobb seemed pretty well established as a person who could retrieve information through dreams at that point. Too well established and familiar with life on the run if you ask me for it to have just been a few months if you ask me.