((((( SPOILER ALERTS(((((((
Well, the premise is that we (the audience) are there to see Wayne Szalinski receive an award for his shrinking invention. Of course, he is his normal nerdy/corny self and accidentally shrinks the audience.
His youngest son, "picks up the audience" there is a sensation of being moved about, accomplished mostly through camera angles.
Wayne also created a duplicator machine. Youngest son puts his mouse, photon into the machine and suddenly there are 100s of mice being recreated. then there is some sort of electrical outage, so the whole thater gets dark. And you can "hear" the mice squeaking around. Also, there is some sort of contraption built into the seat that "tickles" the back of your legs (creating the sensation that there are mice running on the floor). It's quite convincing and it does scare some children.
Another part does feature a large snake and it "spits" as I recall resulting in a bit of water sprayed on you.
I would say this might be an attraction to avoid but if you must go . . .
placing child on your lap would get rid of the additional "sensations' and asking him to close his eyes would relieve seeing all of those things, however, would still have the "sound" and that alone might be enough to drive him crazy!