Genius?

I know every parents think their kids are smart and so. But I wonder whether this is really unusual, or it is common for a 4-yr old.

After dinner last night, Yaya was asking for some snack. I randomly asked her while providing her the snack"if I give you two and Peter two, how many all together I need to give""Four". She replied without thinking. I went on and challenged her"what if I need to give daddy two as well?""Six" "Then if I give myself two..""Eight" At that point, we became curious how far this game could go. I began to use different assumption about giving snacks, and at the end, we found out that she was able to do adding and substraction under 10. I was stuned, Lei was excited. Isn't it amazing? At least she is better than her parents.