Gene Simmons of the band 'KISS' currently owns the prop severed head of the kid's mother. It was given to him by Tim Sullivan when he interviewed Simmons for "Fangoria" in 1983. Sullivan - who was a PA on this film - went on to produce Detroit Rock City (1999) and write and direct 2001 Maniacs (2005) and Driftwood (2006).
There's an unofficial sequel, Metamorphosis: The Alien Factor (1990). In many parts of Asia, it was distributed under the name "The Deadly Spawn 2: The Metamorphosis". Because Metamorphosis was made for millions of dollars more, and had much higher production values than the "Deadly Spawn" did, the producers of both films wanted to separate them altogether.
The effects of the mini-spawns slithering across the floor in the basement was achieved by cutting a "S" wriggle into the floor, and pulling the spawns along under the floor.
The mother spawn was constructed in the basement of effects artist John Dods. However, no one took the creature's size into consideration, so when they had to have it on set, they had to cut off one of the creature's heads to get it through a doorway, and reassemble it on set.
This film was almost picked up for theatrical release by Paramount.