I felt a bit strange about putting a photo of the girl child in a cossie on the internet, but I wanted to document this momentous (to me) first attempt at swimsuit making. You'll have to make do with this slightly weird taped-to-the-wall picture and trust me that it's an excellent fit - no gaping at the legs or chest, but no red marks from too-tight elastic either. It is, of course, the Cosi Swimsuit pattern from Sewpony, and an excellent pattern it is, with lots of different styles included and great instructions for swimwear novices. I made VIew D in Size 5 in some swimwear lycra and fully lined it in swimwear lining, both from Remnant Warehouse. It was very simple to sew, although my overlocker didn't like attaching the elastic, so I did that on the sewing machine and then used the twin needle for top stitching.
It's quite hard to find swimwear for little girls that is cute, age appropriate and not covered in licensed characters so I can definitely see myself making more Cosi's - the pattern goes up to size 10, and each costume uses so little fabric that they're not expensive at all to put together, and a lot of fun.