It would totally depend on the mother cat. If she knows you very well & is relaxed with you...then you can gently touch them after a day or so (you must make sure you really scrub your hands first)
Carefully monitor the mum cats reaction & don't try to take them out of her eyesight for a while as she may feel the need to move them to another location if you disturb them too much. Some cats I've found just want the reassurance of having someone around to fuss them...so make sure you make a real gentle fuss of the mum first.
Don't forget that newborns can't see that great for the first few weeks (relying on smell to find their way) so give them a light touch and talk to them when you are about to pick them up.
Have fun!
when i saw that my cat was having her kittens I waited till she had finished and put my hand next to her I didnt touch any kittens but the mother picked one of them up and put it in my hand, which was the one we kept, just put your hand next to mum and see what she does she'll let you know