Off to the vet for sure! Losing that much hair, especially in clumps, is NOT normal. I would also ditch the flea collars, not only are they not really effective, but they can make them sick as well. It might be time to switch to a new brand of flea topical, as they sometimes lose effectiveness (the fleas/ticks grow immune to them) We used Frontline for a long time but it's stopped working for us so we switched to K9AdvantixII. No more fleas
If your baby has a flea allergy (both of mine do!) then that could explain the bald spots. All it takes is ONE bite from ONE flea and both of my kiddos are miserably scratching themselves silly
My Luna developed a skin infection from all the scratching and while I didn't see the hair lying around (she's kept very short on her body) she started having these lighter patches near her rear end. Once the antibiotics got rid of the infection and I started supplementing her food with Flea Treats and Coconut Oil, it's all grown back.
But anyway, sounds like vet time to me
Good luck and I hope your little one's issue is resolved quickly