Sorry sweetpea74 I have been offline because I hurt my neck & shoulder & couldn't sew / couldn't type -- very boring. I will put some pics up so you can see what they look like on & give you a quick idea how they are made. If you like I will write a proper tute & take a pic of them not on my daughter when I am fully recovered.
Here is the first pair I made when my daughter was 8 months.
& then this pair made out of an old Benetton jumper I got at the markets.
I just placed the leg of a pair of her pants that were a good fit over the jumper arm & then just cut the j-shape for the crotch. The arm seam I left. Then I sewed up the crotch, sewed a strip of cotton ribbing to the top and turned to the inside to make a tunnel for the waist elastic.
The next year I used the body of the jumper to make her another pair. She is still wearing these ones. People always ask about them when she wears them.
Couldn't resist sticking in a picture of yet another pair, she is still wearing from last year (my daughter is 2 1/2 now). I just gave them a good pull when they were wet to get back some length and get rid of the nappy bum shaping now that she no longer wears nappies.