There are a number of reasons your yard could be attracting mosquitoes. But most often it's water. Mosquitoes need water to lay their eggs. So they look for the tiniest bit of water to breed, develop and emerge. Getting rid of standing water anywhere you find it is one of the best solutions to fight mosquitos. Check these spots after a hard rain and make sure they are empty or drain them.
Tire swings
Toys
Flower pot saucers
buckets
Kiddie pools
Trash can lids
Wheelbarrows
Birdbaths (If you have a birdbath in your yard, make sure to replace the water in it at least once a week to keep mosquitoes away)