How can you protect other children in your house from one girl who have herpes?

For genital herpes no special precautions are needed. Genital herpes is only transmitted by having sex with someone who has it. It is not transmitted by normal day to day contact.

Oral herpes (cold sores) is transmitted by kissing, particularly 'deep kissing'. Avoid kissing at all when symptoms are present. Also avoid drinking from the same glass. Transmission isn't likely in either of those cases but they are good general precautions.