A 3 year old doesn't always have an attention span for an age-friendly movie @ a theatre. This movie will have a lot of action, fast scene changes, loud noises, & unrelatable material for someone so young.
Chances are you will spend most of the movie worrying about your son, & not enjoying the show!
If you decide to opt out, DON'T offer or accept watching everyone else's kids. You have the week ahead that you need to be on your game for, as a M., employee & wife. Don't wipe yourself out just because people think you are now available to watch the child they would otherwise have taken to the movie.
Maybe you could find a sitter to watch him just during the movie - take him to a nearby playground & meet you back @ the theatre... maybe the "payment" would be a movie for them w/popcorn following your show!
I appreciate that you are putting your son's well-being first, & not just taking him because "everyone else is doing it". I can't imagine the other young kids will do well with the movie, & as someone who doesn't go to movies with kids, I would hate to be in the same theatre as all of them! (Despicable M., different story, the kids added to the fun!)
Hope things all work out for the best for you & your son/family! T.