Im not sure how to tell, they are kittens and a little shy. But they didn't run away from me, just a little timid.
I noticed another kitty by them just now who wasn't full size looking, but definitely older. He popped back over fence to neighbors house. Kitties seemed to want to follow, but started frolicking in yard in front of me instead.
I'll give them some distance and just watch for now, but I'm pretty sure it's just YET MORE kittens from neighbors pet.
I get frustrated with neighbors that let this happen constantly.....but it's not the kittens faults.