Tulum is a great destination for families with open minds. There will be no television to plug in the kids, and most of the small hotels (AIs excepted) do not have "kids clubs," so this is real family bonding time. There are a variety of outdoor adventures  to keep busy and have fun.

What to Bring

Insect repellent (preferred brands might not be available)
High SPF sunscreen
Favorite beach toys or other favorite toys

What to Do

Sea or cenote snorkeling
Jungle tours
Turtle watching during the nesting season