That would be nice and it's often suggested (in one way or another) already!
I think to have growing up children one has a lot to consider: will everybody else get old too? will Jas, Vincent and Leo grow up to adults? Will elderly people gonna die?
What's happening to the Bachelors/Bachelorettes? Will they marry in PT? Will they leave???
Who's running school (esp. if Penny's leaving)?
Will grown-up children stay in PT and if so where? will they leave??
There can be a solution for each problem, of course. But it's a LOT to consider and even more to implement!
Maybe the Wizard has a spell of youth so nobody has to die.
Maybe Jas, Vincent and Leo grow up and leave for university.
Maybe Bachelors/Bachelorettes marry their former best friend/other Bachelors/Bachelorettes. Maybe the leftover leaves to town...
Maybe Dr. Snail runs school.
Maybe ones own children left too for work/university etc.
Maybe, maybe....
Anyway: implementing such or other stories is a LOT of work!