I used an Enid Gilchrist romper pattern for the leghole area and as a guide for the length of the body. I'm not sure on the sizing but I'm going to say it'll fit her when she's 6-9months, depending on how chunky she is.
It has a sweet-heart neckline that I faced, then added two rows of peach ric-rac. The straps were sandwiched between the facing and the sunsuit and are just knotted as a halter.
The back has elastic in it, to keep it up. I really want to buy some elastic thread and I'm considering shirring across the back? I do like the baggy puffiness of this though. The legs are just elasticated.
And the inspiration: