The kitten came back again this afternoon, meowing its head off and trying to squeeze through a whole in the fence that was too small for it. I approached the kitten from a different direction, but it took off again and ran to the other side of our backyard. Apparently there's a whole in the fence just big enough for it to squeeze through there too. I went out to the front yard, but again no sign.
After they kitten ran off, I peered through the fence and the mother cat was peeking out from under the porch because she had heard her baby calling for her. When I went out to the front, I tried the gate next door and it was unlocked, so I opened it a little bit. Hopefully when the kitten gets brave enough to try to come back into our yard, it'll see the opening to the other yard and find its way to its mommy.
I feel so bad for the little thing. It's terrified and hungry, and probably cold too because it's windy today.