They don't jump just move around. I have found them in his belly and under his legs. At first I thought they were fleas but they are longer and seem to be black.
May God bless you for taking him in!!
What you are seeing may be a stage of flea or mite:
Advantage does not work right away regardless of the dose.
I am so sorry your babies are troubled with fleas. You dont need any harsh products.
You can see a comparison of flea products here
All you have to do is put down some Diatomaceous earth in your yard and a few pots in the house and you and your baby will never see another flea, fly, worm, etc.
Get it at a garden shop or online:
I am in Florida where fleas/bugs/worms are active 24/7/365 and it works like a charm for me.
I hope your baby gets relief very fast.