Shared parenting - holidays

My grandsons at ages 2 and 5 often come to stay with me for a week (the older grandson sometimes comes for longer), so I think a week without mum is quite reasonable. Dad isn't a stranger and however awkward the parents' relationships are I see no reason why it should be a difficulty for the children. Children really are very adaptable.

Nina it is an issue when the relationship between the parents is difficult. I just want to know what people think is reasonable.

I don't think there's a definitive answer. It all depends on circumstances and relationship between the parents.
Ex SiL wanted to take 5 and 3 yr olds to Europe to visit their other GP at Easter in the end he couldn't due to unforseen circumstances but DD was happy for them to go for a week.
Her thought was as he only had them one night a week it would do him good to have to cope as other GPs work full time

A friend of mine is in this situation. He's looked after his son regularly and from the age of three was taking him on holiday for up to a week at a time. By the age of 6 or 7 he was taking him for a fortnight's holiday.