When Malcolm gives Caroline the hamburger she eats nearly 2/3 of it but then when they show her eating it again there is only a bit of it gone.
The family drives a 1990 Dodge/Chrysler Grand voyager minivan. Those cars have middle bench seats that only hold two people, seat-belt (lap only back then) and all, yet in whenever they show numerous family members in the car there are three people in the middle seat. How can the people in the way back get in or out?? (Source: had a dodge grand caravan around the time this 1990 version was popular.)
"In 'Forwards Backwards,' it said that Lois is allergic to nuts. If that is so, how was she able to make the almond brownie?"
The brownie contained walnuts and The Krelboyne Circus (Season 1 Ep 8) preceded Forwards Backwards (Season 4 Ep 5) by thirty-three months. Lois could have developed/discovered the allergy later.
When the Krelboynes run away after Stevie's project explodes, a camera man can be seen chasing after Malcolm for a shot.