Teach your kid to respect a cat’s space, tell tale signs a cat is afraid or angry, and how to approach and pet a cat.

Make sure your cat has it's own space away from or above the baby.

All of the above, and apart from that - it's a true blessing to grow up together with a cat. We got ours when I was four, and teaches you a whole different understanding of respect, empathy and kindness.

Just as general advise, don't use your hands to play with the kitten. It may be cute now, but that's how you get cats that attack feet and hands thinking they're just playing. Get a lot of toys. But then do get the kitten used to you handling her paws while you're gently petting it, that way you can trim the claws later.

Let them bond. The cat is still young and will play a lot and there will be scratching regardless of age, however the cat will learn to not harm anyone as they grow. Your kid may get to a point where he plays a little rough, if he/she does teach them that the cat is not something that should be hit or thrown.
Along with what most people say, leave a small space for the cat to get away from the child when it is done playing. This applies to many animals, not so much dogs since they are playful things but even they require rest every once in a while.

I would find a new home for the three year old

Just keep an eye on the little one when the kitten is around. They'll be alright. *or get a dog instead :-p

My baby loves to watch the kittens run around, and cats of any age are usually pretty good about removing themselves from situations they don't like. As stated above, have a safe space away from everything for the kitten to acclimate and be able to retreat to, and definitely teach your kiddo how to interact with animals. Kids are really smart, they'll learn fast.
I think it's best to teach kids about animals when they are little anyway, and at 3, you should have plenty of comprehension and you can start teaching empathy and compassion!

Thanks for the advice , you really helped me make the right decision. My son has already fallen in love with her so we decided to keep her.

On the practical side of things: Make sure she has all her shots/vaccinations, do NOT let the cat outside at night, and keep your son out of the litterbox
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Honestly having animals around kids is very beneficial for the kids so it sounds like a good thing to me