I have a male kitten and I found him and 3 sisters of his abandoned. They were starved so badly they couldn't last a full day. All of his sisters died so we got him a friend. They play a lot then they get sleepy. My question is: When he gets sleepy, why does he suck on a blanket we have? Is it because he didn't have a mom when we found him? He was about 1 month old, possibly less, so I thought maybe he sucked on the blanket because he never had his mom, but I just want to know why he does it.
Most people would say it's because their mother never made them stop either because the mother died, got lost, or left her kittens. I think this is the truth and could be the issue going on here since you found them.
The reason they do it is because to get fed by mom they need to suck on the nipple, just like human babies. Normally, the mom would teach them to stop, but in this case she never did.
I wouldn't agree with people saying it isn't harmless. Yes it seems cute and innocent but it isn't. The cat can choke or get stomach problems on materials, wool, inner stuffing etc. Some cats will grow over it and stop, but most won't. They do it like children biting on sweater ropes.
Best way to stop it is to either go the hard way or the easier way. The hard way will be trying to pull the cat away every time he does it but since a cat has a big will of his own it's very very very hard to stop it like that.
The easier way would be keeping the cat out of range from cloth for a while so he can't find his addiction to cloth. Remove cloth materials from the ground, walls, couch etc. If the cat sleeps on you, it could be wise to start locking him out for his own safety. Yes, he will meow at the door, start scratching and might even try to open the door with force. For this, you need to ignore how heartbreaking it might be, he wants to be with you because he always have been with you and doesn't understand why you locked him out all of a sudden.
After about 3 months, try to see what he does. If he does it again, repeat else your cat will be fine again to sleep with you without choking himself to death.
It worked for my cat at least, and he doesn't suck on any cloth anymore not even if he is able to do without prevention.