I have a 6 year old who is tall and skinny, 45 lbs, but about 46 inches. Her waist is probably closer to a size 5 so the slim option and the buttons are a must.
We have tried 5 other brands and this one is the best fitting slim we could find. If you have a tall skinny kid you need these! We do have to use the elastic but they don’t seemed as bunched because they are already slim fitting so no super bulky bands coming out the sides.
They are wrinkly so you they don’t air dry well. I have found if you air dry, then run for a few minutes to get the wrinkles out after drying to help prevent fading and shrinking in the clothes so they look better longer.