Add product pages to only child category - not parent category

Hello, Looking for advice - we have just built a new website using expression engine. We’ve roughy 800 products. We imported these products. Now, we have category of products then each category has sub-categories.

Our web design agency have done the product upload but we now appear to have “duplicate” pages for all products because every product appears in the child category as well as the parent category. However, the URL for each page is different. Our design agency have instructed us that this is normal for expression engine but i’m not convinced.

As a work around they are instructing to set up a re-direct of all products to ensure search engines know which is the page to be indexed. They stated we do not have “duplicate” pages because it is one product page in the CMS but expression engine delivers multiple paths to get to the product. So, it shows it under the parent category and then the child (sub-category).

Could someone let me know if this is correct or is there a better way to sort this?

Much appreciated!

Thanks