People are more influenced by their ‘peers’ than anyone else. If ‘everyone’ does it this way, the fact your parents didn’t do it this way, means nothing.
The idea that everything done by your parent is ‘old fashioned’ or ‘out of date’ drowns logic.
As the Grandparent, it is pretty likely your child survived childhood and was functional enough to get married and have a child.
But forget about obvious logic.
If your child’s peers are slathering their babies with mineral oil, your child will use mineral oil. If they use fish oil, your child will turn to fish oil.
That you used coconut or olive oil, and your child has perfect skin, does not mean s/he will look in a mirror; no. If the peers use motor oil on their children, so will your child. To try to force light into darkness is a waste of breath.
Just smirk and talk about the weather.