Grandpa's Talent

I have recently noticed a new talent of Grandpa Frank's: rocking children to sleep. Basically he makes a lap, he rocks, then he leads by example & the children do as he does. This is not the first time we have come home from a night out to this situation. I also recall a few other similar incidents like this one, for example:

Same Grandpa. Same talent. Same chair. 

Is Grandpa the baby whisperer, or is this just the world's most soothing chair?