I had two young adult sims who had a kid. kid aged up progressively from a baby, to a toddler, and to a kid as normal. then when it aged up to a teen I made the personality adjustments and hit continue and all of the sudden it aged up another time to a young adult, then to an adult immediately after one another. all at once. The kid is literally now older than the parents.
sincerely pissed off sims lover