wetting the bed is only common in children under six, after that it is a psychological issue, and even for children under six it is considered a developmental delay. to me the sim kids look at youngest 8 or 9. that makes me uncomfortable, personally. i don't find it funny and i don't see how it is necessary or interesting.
anyway, i don't let my sims fart or soil themselves. how would they make this wetting the bed thing preventable for those of us who don't like it? without forcing us to train toddlers? i skip the toddler life state all the time, they are a massive pain.