This hack might be what you're looking for, but just so you're warned, several people have had troubles with it.
It's also possible to spawn the toddler or baby with any type of spawner, like the ones
here. It is possible that things might screw up when trying to get everyone back again, just so you're warned.
My method (which I've not used for a while, and which is best for photoshoots or any type of storytelling) is to tend to send the rest of the family on a vacation, save if needed, spawn the toddler or baby, take photos, go back to the vacation NBhood without saving, go back in, and send the family home. The babies will be waiting at home where you left them.