Also, all but Bardot are Scandinavian designers. Bardot is Australian. I think the simple designs that rely on the lines of the garment and fabric choices, so common in Scandinavian design, lends itself to being tween friendly. Most tweens don't want all the frills and ruffles anyway.
And Peek-a-Boo patterns just came out with a jumpsuit pattern as well.
There are so many options when it comes to jumpsuits...
|Serephic Raglan by Figgy's|
|Skipper Top by Sew Much Ado|
|Burda Style free pattern|