The actor, who has 10-month-old twin girls called Dolly and Charlie with wife Rebecca Romijn, said that they can't believe how different their personalities are.
O'Connell is quoted by MSN as saying: "One is go with anything, you put her down, she's cool with it. One is just a little more demanding, and wants her way. If you have something shiny near you, she wants it and if you don't give it to her she gets very upset."
He continued: "I shouldn't say which, but one is a little more diabolical than the other one, but I like that, it shows spunk."