What foods should you eat for a bigger legs and butt?

You cant make your food target areas of your body. You can put on weight and it will disperse itsef all over. Different people have weight concentrations in different places (butt, hips, stomach etc). but by putting on weight you will gain at least a little bit in all places.

If you want to increase the size of your butt and legs i suggest you start adding muscle in those areas by weight training. Try doing squats and crunches , using stretch rubber bands for resistance or taking dance classes. Other great ideas include bycling, rollerblading - or for the fastest most targeted results - visit the gym!