Tom Selleck has two children: his daughter Hannah (born December 16, 1988) with his wife Jillie Mack, and an adopted son, Kevin, from his previous marriage. (Wikipedia)
There are some secondary or tabloid-style reports that call him a “grandpa of 6.” (Daoreuk) However, I found no credible mainstream interview or reliable source where Tom Selleck confirms having grandchildren.
In a profile, The Washington Post describes Selleck as having “a grandfatherly air” at age 79 – but this seems to be a metaphorical description, not a statement of family status. (The Washington Post)
His memoir (mentioned in recent press) focuses more on his life’s journey, career, and his relationship with his daughter and ranch – it does not clearly state he has grandchildren. (The Washington Post)
Conclusion
As of now, while some lesser sources claim Tom Selleck is a grandfather, there is no strong, verifiable confirmation from reliable media or from Selleck himself. It’s possible that the “grandpa” label is more figurative – referring to his age or demeanor – rather than literal.

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