We own 3 weeks at the Royal Sands in Cancun, (24, 25 & 26). We have been vacationing there for 8 years since our youngest was just under 2. It is a wonderful family resort, very safe with lots for the kids to do.
There is a laundry room open, Monday - Saturday, 7am - 9pm. It costs about $3 per load to wash and dry, with a nice tip, Olivia will even fold everything for you.
It is usuall in the 90's in June, but we don't seem to notice it as we are usually in the pool or on the beach all day long.