When in doubt, just remember your manners.
It is impolite to be a guest in anyone’s home and comment on the untidiness of it. You are a gran, not a resident. You must still mind your manners while in their home.
Please remember that your visits are a choice. If you do not like the state of their home, you can choose not to visit. If you want to continue to visit, just be polite.
However, I don’t think it’s rude to ask family if there is anything you can do for them. Leave it open-ended so that if they do want your help tidying they can say so themselves. In that case, have at it!
Being a gran is a dance between being a solid support and biting your tongue, imo. Life is great after you work past the missteps in the beginning—which we all make. Just get in as much time and cuddles with the little one as you can! Your son and dil will be fine 