If your child (and I live with three of 'em) is dead-set on messing with your drivers, the dowel tweak certainly won't be of much help.
Fostex makes metal mesh covers for their drivers, the sort one might see in an automotive use. I don't know what effect this would have sonically, but I know it would take a pretty crafty three year old--not to mention a Hex wrench--to get at the driver with those in place.
PS: I've found the best "tweak" to keep kids, animals and even guests away from my audio gear is abject fear. My sons would sooner sit on a hot oven than touch anything in my listening room. You know what they say...
"Spare the dowel..."