My daughter has been wearing these since she started potty training at around 22 months.  She is about 2.5 now and still wearing the 18 month size.  She is a little small for her age and still has some room to grow in these.  She has warn some different brands and styles home after an accident at a friend or relative's house and she asks to put these on as soon as she can instead.  They seem to really comfortable to her.