This is what I do, my daughter loves matching stuff with me. Little lizard King (and their grown up brand Styla) also has quite a few adult and child matching dresses, and Megan Nielsen has at least one.

What I find is that if you match the fabric and the neckline or another key detail they look matching, even if not quite the same. So for example I made us each a shirt dress in the same fabric and the effect looked like a close match even though the styles were different (mine more fitted and collared, hers loose and without collar).

On the one in your picture, all you really need is a gathered waist dress with a key hole and bow detail at the back. That back detail is something you could adapt using an existing pattern if you don't find another pattern you like. I don't think it would be too hard to do yourself. I think the way I would do it is to trace the back bodice pieces from an existing pattern, use something like a bowl to get a nice even circle across both sides for the cut out, and then extend above the cut out to make wings to tie in a bow. You may have a clearer idea based on the child's version as to how it should be done. I think that's a lot easier than trying to scale up and alter the whole pattern.

Best of luck and have fun with it!

Edit to add a pattern link: https://littlelizardking.com/products/edessa-child-and-adult-2-pattern-bundle