As long as you hadnt used the cheat code to turn off aging, your newborn/toddler will age just like a nomal sim. Newbor > Toddler > Child > Teen > Elder
i tried... i bought them a cake and stuff.... they just blew the candles and that was it. they never grew up... :/
that sometimes happens when a toddler is very tired, since i have the boolprop cheat on most of the time, i just adjust their 'sleep' need & click on the baby picking 'help with birthday' this works (after the adult is done staring at the distance for a while, probably figuring out how throwing the baby into the air again will in any way help it have a birthday), but other wise i guess you'll have to wait till the baby is rested to try again