Why are my Sims' base body templates changing?

Happens to my sims every time someone in the active household ages up or has a baby and it's driving me insane! I've set some stronger limits on MCCommand center to fight it but I don't understand why it's happening... My female frame sims get a huge belly, maxed out shoulder width, and * down to their belly button while Male frame sims get tiny feet and huge hips (other body parts change too but are less noticable)