Do the cats look thin? If so, they've probably been abandoned. Do they look young? The younger they are, the better they would do living inside. If you catch them, have a vet check them to see if they've been micro-chipped...if so, the owner may be able to be found.
I came home late one night and a kitten came out of no where and grabbed my pant leg this past July. I picked him up and could feel he was too skinny right away. I took him in the house and fed him (I have 2 other cats so have everything needed for another, lol). I've never seen a kitten eat like he did. For three days he noisily inhaled his food, getting every crumb... and then looked up at me like he was so grateful.
I had the neighborhood kids helping me for 2 weeks trying to find his home. I called all the local vets, shelters, rescues and nothing. After 2 weeks, I took him to my vet. He wasn't micro-chipped so I told her he had a home with me then and he's gotten all his shots, neutered & micro-chipped since.
He has been an awesome little guy, I'm so glad he found me!! I tell everyone and I've had quite a few people tell me they got their cats the same way and they said their cats are so good, it's like they really appreciate having a loving home after knowing what it's like to be without.
So...if you can, keep them. If you can't, try to find them a home with someone that you know would be good to them. Save the "rescue" & "shelters" as a very last resort and please do NOT post them for "free" to the public (they might be taken and used as bait for fighting dogs or sold to a lab).
It would be alarming to see two little kids alone on your property, yet that's what you have. Two kids with an extra two legs, in fur coats. If their parents can't be found, they need you help in finding a safe home.