Other kids holding my baby

Just curious what other moms opinions are about other people's kids holding their child. My baby just turned one month and I absolutely don't want any kids holding him! My sister-in-law does not seem to understand this even though she knows it bothers me. She gives my baby to her 6 year olds to hold! She said I need to realize it's ok for him to be exposed to germs. I don't want to be a bitch but I'm on the verge of snapping! Am I overreacting? My little guy hasn't even had his shots yet.