Expecting DS1 very soon and starting to think about when he's here.
OH's parents already have grandchildren from his siblings. When their first grandchild was learning to talk, they mispronounced 'Granny' and 'Grandpa' (as young children often do) it was cute and funny at the time but the in laws encouraged it.
Now, several grandchildren later (all at an age of speaking perfectly well) they all still refer to their grandparents as these mispronunciations.
It really grates on me - I come from a child education background so I know how frustrating it is when children use alternative words for something and teaching children to mispronounce a word is a big pet hate of mine.
So, AIBU to ask them to stop this for my child? It's not a habit I want him to fall into and definitely not something that will happen with any other family members but it's clear they like it as they've done it for years.