Answer:
If you hold them when they are still depending on their mother , it will cause her to reject the babies, because they rely mostly on there smell. The mother will think the babies are intruders because they have YOUR "smell". I would probably say the right time to hold them is about a couple a weeks. Two or more weeks would be fine. The mother won't reject the babies then. To be safe you should play with them when they have a layer of fur to cover themselves. (I had about 50 babies, but I DIDN'T want a hamster farm). I never had a baby rejected though. Mom hamsters can eat them to, but very rarely. (They have to be starving too) I think that moms rejecting them is very VERY rare. If you have Roborovski's you should look at Roborovski hamsters, a site completely devoted to Robos.