RICHMOND, Va. (WRIC) -- The back-to-school season is behind us, but you might’ve had your kid come home with a runny nose or cough. The start of school can be tough on the immune system, especially for the little ones. As soon as those start-of-school germs are dying down, cold and flu season comes in with fall. But each day, students’ immune systems can get stronger.   “We really really really go hard with the handwashing," said Felicia Richards, a lead nurse for Richmond Public Schools. “Our three-year-olds really get hit the hardest. Their immune systems are just now getting ready.”  It's Richards's fifth year with the school system. The start of the school year is the perfect breeding ground for germs, and some experts call it the back-to-school effect. Especially for little ones, like at the Maymont Pre-School Center.  “They hug each other; they touch everything," she said. Immune systems can still be considered immature until six or seven years old, building their library of resistance. “As soon as you notice your child is not acting the same, you see fevers, any vomiting, any new rashes, anything like that, just keep them home," she said. “If anybody has a fever, they have to stay home and they have to be fever-free for over 24 hours.”  Richards said the traffic to her office does improve as the school year goes on and immune systems build up.   ...read more read less