This is what I would do if I were you, but keep in mind I suffer from AmigaMania...
A4000 stays as the dad computer. A1200 can be mum's computer, and the A600 is son's computer. One A500 must stay set up for classic floppy gaming, and the CD32 (especially if you keep the SX-1 and pack a CF card full of WHDLoad games selecable from a menu) would make the perfect games room Amiga.
Sell or give away the others to someone who can repair them and make use of them. Install plenty of games, as well as creative software on the A600, like Deluxe Paint and SEUCK. Your little feller can grow up not only playing games but making his own.