My little guy would not leave his undies on. NO matter how many times we let him pick out his own character briefs, he just didn't like the feel.  My friend mentioned boxer briefs and said that's all her boys would wear. So I gave them a shot and he loves them! He leaves them on ( most of the time). I usually can get these at Walmart for about the same price but they have been sold out of his size. I was happy to find them on amazon.  Wish there were more color choices and characters like they offer with toddler briefs. But as long as he leaves them on then I am a happy mama. They are soft and wash up great. They tend to stretch out after wearing. So if they seem too small when you first take them out of the package then I would recommend washing them up and giving them a try. Chances are they will stretch out and fit perfectly. My little guy started wearing these when he was just over 2 1/2. He was wearing a 3T at the time. I ordered these in a 4T based off the size chart on the package and they fit perfectly.