I was wondering is a wbc of 15 abnormal for a 4 year old?

Need more info!: I assume you mean 15,000. It can be normal, as kids tend to run a little bit higher total WBC count than adults do. But you need so much more information including the different types of WBC's present and their ratios, and then correlation with the clinical picture. Who cares about an isolated number if your child is running around healthy and happy!