My 1 year old son has a rash all over the body and face, what can I give him?

May not need anythin. The whole body rash implys a whole body issue. Possibly a simple entero (stomach)virus that ended in a painless flat pinpoint rash as it ended, or consumed a product that resulted in itchy bumps all over. A new shampoo or bath soap/detergent etc could be an issue. For major itching a cool bath or teaspoon of benedryl/25lb might be indicated short term. If no itching do nothing, it will fade on its own.
Depends. At 1 year of age, this is very likely to simply be the result of a cold virus, and nothing you really do will help it....Just time. However for any sign of illness (fever, not eating/drinking, sleeping too much, crying constantly, etc), or if they started any new medications recently, the child needs to be seen asap.