Having flown a few times with my children, may I offer some advice.

If you have time, grab some nice chocolates and offer them to the FA as a peace offering while getting settled in on the plane before take off. If no time before take off, offer them as soon as possible. This will be handy when asking for a bottle to be heated later, etc...

Consider Y cabin with a separate seat for the little one and a car seat or CARES harness. Much safer. Lap belt loops can actually be worse. In an accident, a baby belted to a parent can be crushed on a sudden impact as the adults body goes forward and the hip angle decreases.

Bring things to entertain the child. Stickers, toys, tablet (with kid earphones that are small enough for them), plush animals, books, etc... NEW toys are great as they will hold attention longer.

Bring food, Airlines often forget kids food, and often it is not something they like or are used to. Baby meals are usually the jarred pureed stuff, which most 18 month olds couldn't care for.

I actually keep stickers on my carry on at all times. I had one loud child behind me. So I got up, got my carry on out, pulled some stickers out, and started talking to the kid (just under two) and offered the stickers. The kid quieted down and the tray table on the back of my seat was full of stickers. Better than crying and screaming. It was only LGA-YYZ but it was worth $5 at the dollar store for the quiet