Evidently that’s a child being taken on the left side:

https://www.reddit.com/r/starwarsrebels/comments/7fpf31/spoilers_fpj_discusses_season_4_on_the_forcecast/

Now the obvious theory is the child is Kanan and this is some kind of prophesy. One might say too obvious, but who else could it be? It can’t be Ezra; he wasn’t taken by the Jedi.

It’s a crack theory right now and probably absurd, but I can’t help wonder if Ezra and Kanan are related.