Can the college students from sims 2 have kids? Can the teens?

Two of my college students are engaged. But one day when I wasn't paying any attention they slipped into the bed you know to do there thing, and I ended up hearing that little baby lullaby but I have been waiting days for the baby yet it still hasn't come! Now I'm just wondering if they can have kids yet or if they'll have to wait till they transform into adults. PLease comment! Tanxu.