SAN MATEO COUNTY, Calif. --There will be smiles all around San Mateo County this Friday. That's because dentists will be offering free service to children from low-income families. Friday is 'Give Kids a Smile' Day.'Eleven dentists are offering 112 free appointments to residents ages one to 18 who otherwise couldn't afford the care. You need to call and make an appointment. The number for the San Mateo County health coverage unit is (650) 616-2002.