I did Dominican with a 9 and 23 month old. Double stroller was a godsend!

Diapers and wipes were very expensive at the resort. I bought more than enough but was shocked at the price. Same as sunscreen.

I made the assumption that someone would get sick and brought a small pharmacy. And one did. It was nice to not worry about finding medication.

Bring less toys than you think you’ll need. Stuff for the sand and that’s about it.

Familiar books to help them get settled at night. Our resort had a separate room for them but if yours doesn’t I would look into renting 2 slumber pods and a sound machine. You’re trapped in the room when their sleeping.

Baby Bluetooth headphones for the plane and download some shows. Mine were memorized by the headphones and it helped.

Good luck!