For a beach day, I recommend Mr Sanchos or Paradise Beach for families. Lots to do with kids including the inflatables on the water. Both have an all inclusive package & you can book online. IMO Playa Mia is not as nice and the food there is pretty bad. There are tours of all of them on YT so you can get a feel for each.
If anyone likes to snorkel, these beaches are not the place since they just have sandy beach with shallow water. In that case I would spend the day at Chankanaab Park. Great snorkeling with underwater statuary and sunken boat to see. Lots to see & do in the park & a fun day. Also closest to port.
For any option, just grab a taxi when you arrive. They will have a vehicle large enough to handle 5.
Enjoy!