The waterpark scenes were filmed at Wild Rivers Waterpark in Irvine, CA. The park was torn down in 2011 by the Irvine Company to make room for an apartment complex.
On his way up the ramp to "The Liquidator" slide, an increasingly worried Malcolm passes a series of signs: "Caution!" "Warning!" "Danger!" "Careful!" "Pelligro!" "Watch out!" "Achtung!". As used in "World of Warcraft", "Pelligro" is spelled correctly. As the Spanish word for "Danger", it should be "Peligro".
Dewey and his nanny (played by Bea Arthur) dance to ABBA's 'Fernando'. In The Golden Girls (1985), Arthur once dressed up as Cher, who co-starred in [Mamma Mia! Here We Go Again (2018)], where she sang 'Fernando'.
Bea Arthur states that her imaginary friend is "Harold". Bea Arthur famously played Maude in the television show Maude (1972) while Harold and Maude (1971) is a famous movie.