Grannies acting as nannies are making summer holidays "three-generational", a new survey showed.
A third of grandparents regularly holiday with their children and grandchildren for the sole purpose of providing child care assistance, a study from insurance company RIAS found.
Even when they are at home, 50% of grandparents look after grandchildren during the summer holidays.
A total of 26% of grandparents said their childminding activities were caused by the fact that parents had had to return to work because of the economic climate, while 28% said parents were working longer hours.
The time spent by grandparents looking after grandchildren could cost parents up to £558 if they had to pay for it - saving UK parents around £800 million a year.
RIAS managing director Janet Connor said: "Our study shows that the extended family holiday is enjoying a comeback and that grandparents really are at the heart of many families.
"As working hours get longer and the impact of previous years' economic turmoil hangs over us, it looks as though parents are relying on grandparents more than ever before, especially over the long summer holiday break.
"We expect the trend to grow as families look to make the most of their free time together, and the spare pairs of hands that grandparents provide are certainly a welcome support."
The survey was based on responses from 1,908 grandparents aged over 50.