Continuity mistake: in the scene where Greg comes in to his parents bedroom and they are having fun with whipped cream, there are 2 pillar candles by the door. These candles are seen in several of the shots showing Greg. The flames keep going out and relighting, but the candles are too new for the flame to be just dipping out of sight, and besides those sort of candles will often glow near the top when that happens. They must have kept blowing out between takes and the crew kept lighting them.
Continuity mistake: In the scene where the two sets of parents meet for the first time on the island, Bernie hugs Greg leaving his sweat mark on Greg's shirt which also looks wrinkled. This changes to there being no wetness at all, some wetness and then very wet again in between shots of him. When he enters the house, his t-shirt is totally smooth and dry.