How do I get into shape for the summer?

I am 14, pretty tall (5' 10"), and what some may consider light (120 lbs.). I have no problem with my height and weight (except the little flab I have on my thighs), other than the fact that I am very scrawny. I have been doing about 400 crunches in the morning and night to build up my abs (I just want to tone, I have no desire for a six-pack, or even anything close). I also use my Mom's 8lb. weights (which is the heaviest she has) to do some basic lifting exercises. I have seen some results over the past couple of weeks, but I am still scrawny. Is there an effective, healthy way to tone my muscle and maybe loose what little flab I have on my thighs? I do not want to starve myself or do anything else dangerous.

Thank you a lot!!!!