I honestly don't even remember at what point I started picking up dd1 or ds2 (had c-sections when each of them were about 2). It was sooner than it should have been, and I felt it a few times, but I don't remember exactly when.
All I can recommend is avoiding it if at all possible, for as long as you can. When it's unavoidable, lift with your knees as much as you can, keep your stomach pulled in as much as feasible (hard post-op, I know) and get your toddler moved and put down as quickly as you can without pushing too hard or jerking.
The whole "don't pick up anything heavier than your baby" and "have your older children climb up onto your lap, instead of picking them up" thing makes me nuts. The people writing these guidelines might be experts on surgical recovery, but I don't think they have a clue what it's like to be home alone with a newborn, an older child (or children), and a surgical incision.