I need some advice...

My Nana is going to a birthday party a few hours away on the 25th for a family friend whose son is turning 4, and asked to take my kids who are 4 and 2, I am not sure if I feel comfortable about her taking them 3 hours away with me. I have a 3 wk old I don't feel comfortable taking to a birthday party afraid he may catch something. How do I tell her I don't feel comfortable letting her take my babies without getting her upset.