Here is Aimee's All-In-One Pattern she designed and will be putting on You Can Make This website soon. She asked me to test it and here is the result. The pattern is very easy to make and the instructions are simple to follow. The pattern comes in sizes 24 months to size 6. There is also instructions for an optional ruffle along the top and pants legs. Here is a link to her website for more information and to see pictures of what it looks like on her daughters.
The back is halter style with elastic that can be adjusted for growth.