However, according to Royal London, this is still likely to only be a small fraction of the numbers of people who could benefit.
The claims can be backdated to when the scheme first launched back in 2011.
These credits are added to the National Insurance record of the claimant, which can help them to build up a full state pension.
The FOI was tabled by Helen Morrissey, pension specialist at Royal London.
She said: “Grandparents have long carried out a vital service in taking care of grandchildren whose parents return to work and it is positive that this benefit exists to ensure those under state pension age do not miss out on National Insurance credits.
“However, while it is really positive to see such growth in the number of applications we are still only scratching the surface when it comes to the numbers of people who stand to benefit.