Like mutt said you need to get an oscillating fan on them, and bury the stem right up to the first set of leaves in your growing medium/soil.
Do you have any pics? How old are these?
It is hard to tell exactly what the problem is without more info. Make sure that you keep the floro's close enough to the plants that they do not stretch looking for light. But from the info we have it sounds like they are stretching so much that they are toppiling over.
Just for NEWB info. A fan not only circulates air. it also causes microscopic tears in the stem which the plant reapairs itslef and makes stronger. this ensures that the plant is strong enough to handle the heavy wet weight of the buds down the road.
Florous you can keep within about 2"-3" of you plant without risk of burning them.
MassProducer is 100% correct if it stretched that much pack some dirt around it. and he and redandwhite is right. you need to give us more info. like what ferts and soil mix. you'll need more lights too. Pics are worth a 1000 words as well.
Two factors in plants stretching and falling over...distance from the light source is too great, and circulation. Tube flourescents can be (need to be) as close as possible without touching. No concern of heat "IF" your fan is blowing on them sufficiently. Babies need to sway in the breeze. Fix these conditions, you won't have that problem.