Fleas are not a lawn problem, but they can quickly become a problem for you and your pets. There are several products available that will kill fleas in the yard, however, these products also kill a number of other beneficial insects.
Outdoor fleas are seldom a problem for humans unless you have a large infestation. In that case, you probably should apply a pest control product that includes fleas. However, if the outdoor flea population is not noticeably bad, work on controlling fleas from entering the house where they can become a problem for you.
Fleas are usually brought indoors by a pet. This naturally occurs during the growing season when flea activity is highest. If you suspect a flea population in your yard, but one that hasn't become a problem for you and your guests, then treat your pet for fleas and leave the lawn insects alone. There are numerous products available that provide 24 hour protection for your pet. Check with your vet for the most suitable product for your pet.