This is a pretty simple change to make, so I'll absolutely take requests for additional colors if anyone wants them.
To install, simply copy the XNB files into the Content\Characters folder under your Stardew Valley game folder. There shouldn't be any problems, but I'd advise saving a backup of the vanilla files first, as one always should do when modding.
Eventually I'd like to expand this so that the notification of your child's arrival no longer specifies "baby boy" or "baby girl" and possibly tweak the Child #2 hairstyle to be less suggestive of dual ponytails. That way, the toddlers could truly be gender-neutral and you could have two sons, two daughters, one of each, one or more kids that are simply non-binary... You could play them any way you like. I haven't gotten that far yet, though, so for now it's just the bodysuit colors that have changed.