Flying with a 16 month old?

Hello everyone 👋🏼

My mom booked me a flight just after Christmas to go visit her with my son. I’m 15 weeks pregnant and don’t have much patience at this point lol. Can anyone share with me things that helped keep your child calm on the plane? I’m just freaking out a bit cause I’ve never flown with him at all before and I’m worried about how I’ll keep him still for a four hour stretch. I asked her to book the flight as late as she could find too, so that he’ll be likely to sleep. Really nervous 😕 So.. any tips, advice, words of wisdom? Thanks! 😊