It seems a zombified child wouldn’t be able to bash doors or the like. Probably windows. Just saying. Maybe not have zombie children be able to bash doors.
I personally think that zombies should require several of their number (brutes and hulks nonwithstanding) up against the door to be given the chance to smash it at all. Maybe two or so. Same with boarded up windows, etc. Could be counterbalanced by drawing zombies together when they deliberate to smash stuff, so that it’ll actually happen.
As a side note, wooden doors must be very flimsy if any one can be smashed down by a few blows of the fist, so maybe that’s the issue itself.
SOME doors. but front doors?