He's not a baby he's a pre-schooler. He needs to be allowed to attend activities and learn how to behave. One parent can take him out and make him sit in your lap the entire time you are out of the auditorium then ask him if he can sit quietly. Go back in, when he starts fidgiting in your lap you take him back out and he sits in your lap until he is acting better. Then you go back in. And repeat repeat repeat.
This is how all my friends get their kids to stay quiet during sacrament meeting at church. They take them out and sit them in their lap or on a counter and DO NOT LET THEM DOWN for any reason. They will decide it is play time. Do not look at them or talk to them. It is segregation time. You have to stay there so he will not get up and start running around, he will eventually settle down and sit as still as he can for at least a few minutes when you say "Do you want to go sit out in the hallway?". Then you have reached the goal behavior. He has learned how to act in a public setting.
This may not be completely finished for a couple of years but as long as you are consistent he will learn to sit quietly. If you bring quiet toys for him to play with that will also help. If you do any crafts at all you can look in the pattern books at Hobby Lobby or some other store when they are on sale for $.99 and buy a pattern to make a couple of quiet books.
I will caution you that strong Velcro makes a very very loud noise when it is very quiet...lol.
On of my other friends who now lives in SLC had a method for taking care of this issue too. She would start the kids when they were very small and they had an area in their living room where they had some little seats. Every day they would take time to go sit in the chairs and have quiet time. It was pretty short for the little ones and the goal was to work up to about 15-20 minutes so that in church when the sacrament was being passed the kids could sit quietly. They had guidelines for how long each aged child was to learn to sit there quietly. They did not punish them if they didn't do it each time. They just reminded them when they started the next day that they were expected to sit quietly for a few minutes today.