Unless you buy the extra sides, there is only one setting for waist size. It actually happens to fit my slender 3 year old. But then all of a sudden, she figured out how to use the potty 100% and doesn't need them. Good quality product though, overall.
With the larger flex panels added in, they fit my really tall 4 year old who still needs night time protection. And they will save me a whole lot of money on pull-ups!!
These trainers are great and make a really good alternative to disposable pull ups. Easy for toddlers to pull up and down for potty training. The only reason I'm giving 4 stars instead of 5 stars is because they are pretty tight around the waist which means you basically have to order the bigger max side panels. My little one is small. He just turned 2 and is 23lbs and he needs the bigger side panels already.