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).
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.
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 wanted to separate them altogether.
The trivia item below may give away important plot points.
The character of Ellen, Pete's girlfriend, was supposed to survive until the end of the film. This changed when Jean Tafler, who played Ellen, got another job that was going to make it impossible for her to keep working on this movie. As a solution, she was "written out" of the script in a rather spectacular way, while Kathy (played by Karen Tighe) wound up being the one who survives.