Confirm there are not already settings or features that do what the shop is asking for: No there is no such feature available.

What does the shop want the product to do: The shop wants clothing sizes under a single product listing. Instead of creating separate products for Infants, Toddlers, and Adults, we want to offer all of these age groups as size variants within one unified product page

Why/how would it improve sales or efficiency: By merging them, all reviews pool onto one page. A parent buying an infant shirt with them.