how do you think Kate and Humphrey met for the first time as pups?

Makes sense to me. For the first three minutes of the first film Kate and Humphrey already seemed to know each other and we're in love then and Kate was shown living in the Alpha Family Den. In The 2nd Film when Kate was cleaning up the same Alpha Family den she asks Humphrey to move some log against the wall and Humphrey said "This is where we first fell in love." Implying that the two knew each other a life-long time.