I handled my cats kitties pretty soon after she had them.If you have a good relationship with your puss and she has them in a safe place,she wo'nt mind if you handle them,but I would'nt go messing about with them too much,Mum does'nt tend to like that & it might get her stressed.Plus,do'nt let any Tom,Dick or Harry pick them up,she will trust you as she knows you & your smell,other people she might not be too keen on.
Kitties are a joy to have,good luck & feed Mum up so she can feed her babies well!!