Get a little garage (shed) for their stuff and keep them out of daddy's garage.
Other solutions:
1) Rewire your battery tender for 240 volt
2) Surroud the car with bathtubs or beds. Many children hate bathtime and bedtime.
3) Hide lots of candy in the garage far away from the car
4) It's a little late now, but have you thought of a vasectomy?
Old Hippie Young Heart
2000 S/3.2 Liter/Tiptronic/Boxster S Sport Package/Cruise Control/Slate Grey Metallic
Red Special Leather Interior/Red Floor Mats/Red Hand Painted Instrument Dials/Roll Bar/Windstop
Small Carbon Package/Leather Wrap Carbon Wheel/Center Console Exterior Color/Alum Carbon Shift Knob
AM/FM Radio w/CD Player & Changer/Digital Sound Package/18" Turbo Wheels/Wheel Caps w/Colored Crest