If its 3 days old there is nothing u can buy to de flea it as it is well too young and almost all flea products are well too strong.
U will just have to try your best by combing it.
But with the mummy use stronghold.
It is the best flea stuff u can get and also prevents the cat from getting worms.
Never use frontline or flea powders.
Hope iv helped u. Just listen to the vet.