[[!getResources? &parents=`1,2` &tpl=`productTpl`]]
also, will there be other categories/subcategories/etc. down the road?A better solution would be possible if the products have a different template to all the other pages. That would allow you to add new categories without having to add more ids to the snippet call:
[[!getResources? &parents=`1` &where=`{"template:=":5}` &tpl=`productTpl`]]