Sized very funny

I read many reviews and did my research before I purchased these. I read that the sizing was a little off, so I ordered a size larger. My daughter only weights 19 pounds and usually wears a 12 month onsie. I purchased these 18 month size. They barely fit. They are WAY too short. They barely fit her now, but they definately wont fit her when she is 13 months old.