You talk about two different thing, product titles and category titles, and used them as the same thing in your example.
You should make your product names as unique as possible. It's OK if the category is the same (because that is what a category does), but the product title should be unique.
Example which are fine:
Category Productname (this is what holds the SEO value)
Children long sleeve shirts -> Bright blue cartoon T-shirt
Children long sleeve shirts -> Flashy pink pony T-shirt
Children long sleeve shirts -> Happy squirrels friends T-shirt
If you have this:
Category Productname (this is what holds the SEO value)
Long sleeve shirts -> Children long sleeve shirts
Long sleeve shirts -> Family long sleeve shirts
Long sleeve shirts -> Couple long sleeve shirts
You still have unique titles, but they're very alike and I would not recommend this. It will not hurt you (as long as your content is unique), but it isn't very good either.