No, the baby will NOT grow up beside Benji, i'm sorry to say. Wouldn't it be cool if that could really happen? I think that would be so sweet.
And if you don't want the parent to leave, and this is very simple, JUST PAUSE IT AT NIGHT.
But be warned: PAUSING TAKES UP ALOT OF THE BATTERY.
If ever your son wants to start a new generation, instead of un-pausing it at night, I strongly advise that you FF the time to 11:59 P.M. ( this is done by going to the clock screen and then pressing A and C togeter.) Then, keep the lights on and wait a minute. The parent will wake up, and stare at the baby for about 3 minutes. Then, he will start talking for a few seconds, and then fly away... it's sad, and i have never missed any departuring of my tamas.
Hope i was helpful!
Marie