During the custody hearing, after Laura says that she wanted a Mystery Date board game for Christmas when she was Charlie's age but never got one, Neil says that he was three years old, and he wanted an Oscar Meyer Weenie Whistle. He added that Christmas came, but he didn't get one, and that was when he stopped believing in Santa Claus.
At the end of the movie, when Scott/Santa drops gifts for Charlie, Laura, and Neil, Neil gets the Oscar Meyer Weenie Whistle and blows it with a look of childlike wonder in his eyes.
Neil then apologizes to Charlie for not believing him when he said that Scott was Santa, and Charlie replied, "That's OK, Neil. You were just denying your inner child."