The trivia items below may give away important plot points.
Sylvester Stallone appears in the second season as himself and Kate tells him that her father (played by Milo Ventimiglia) has seen every Rocky movie. This is ironic because Milo Ventimiglia actually played Rocky Balboa's son.
There are a few hints in the pilot that Kevin and Kate are twins and that Randall is their brother. For example, in the scene where Randall gets an email saying that they found his biological father, an email entitled "It's Our Birthday Bro" can be seen in his inbox from Kevin.