how close to the light, and how close together are they? They should be very close to the light, an inch or two assuming you use flourescent. You can thin them out somewhat too. Don't pull them as that will upset the roots of the neighbor but carefully pinch or snip just above soil level. You could even start putting them outside on nice days in part shade to start hardening a bit. That will sturdy up the stems too. Any air current will 'exercise' the stem and make it stronger. If they have true leaves then you can probably seperate them into their own little pots.