i'm playing my first (solo) session of Z9, the Ashes to Ashes expansion which includes child zombies. Obviously, i felt compelled to modify the rules for child zombies, and here they are:
1) When spawning non-dog zombies on a Z9 tile, spawn half (rounded down) of them as child zombies. Place each newly-spawned child in the same space as one of the newly-spawned adult zombies. When a child is paired with another zombie this way, the other zombie is considered to be the child's chaperone. Chaperones provide the following benefits:
2a) When a chaperone moves, its child moves "for free" with the chaperone (it does not count against the number of zombies moving this turn). When a child is moved this way, it does not also move "on its own" in that turn - it stays with its chaperone. When playing solo, the player "should" always choose to move adult/child pairs, rather than moving a child away from its chaperone.
2b) When fighting a pair of chaperone/child zombies, the chaperone must always be targeted first. (The chaperone protects the child, and the child makes every attempt to take protection behind the adult.)
2c) Optionally, if using zombie dogs: allow dogs to chaperone children and assume that children can ride the dogs, benefiting from their increased movement.
3) When a child zombie is destroyed, instead of placing it in the player's collection, put it back in the pool and place a random zombie from the main pool into the player's collection. (This ensures that the game always has a fresh supply of child zombies.) Exception: when the victory conditions depend on defeating some number of child zombies, place destroyed child zombies in the slayer's collection as normal.