My three year old has the same problem!! The only pants I have found that come in slim and tall sizes are at sears, also you might look for pants that have the adjustable waist band built into them! There is a piece of elastic and a button inside the pants, one on either side, the elastic has button holes at different intervals so you can tighten or loosen them as needed! Kind of like a built in belt! I have found these at Target, JcPenney, Old Navy, Sears, Carters, Children's Place etc!! Hope this helps! Also, my son is 3 1/2 now, I have a lot of jeans and pants that he has outgrown if you're interested I can email you some pics!