I was so happy to hear that it is playing with you and engaging. Unfortunately I have had to take back a couple of feral kittens I rehomed that didn't get socialized properly and they are still very skittish at 2 years old.

I'd call your vet and see if they don't have a flea shampoo they can recommend or will sell you. I have heard mixed results about the dish soap method and do not trust the over the counter flea products at all. Fleas really aren't something you want to mess around with not only because of the havoc they wreak on your home but also because they will dehydrate and kill a small one very quickly.

You could also try just washing it in water because I believe the fleas should die from drowning. Good luck!