Why do Grandkids grow up faster than your kids?

Have you ever noticed that grandkids grow up faster than your own children. I guess to be an expert on this you have to be a grandparent but anyone could observe this phenomana. Help me out here. This is a serious issue with me. I had my own 4 kids FOREVER as little tots but grandkids are small one minute and then in college the next. How does it happen? Why don't they take as long to grow up as your children do? My dogs take longer to mature than the grandkids! Any one out there have the answer. This keeps me awake nights and I need my sleep! I will be checking for answers to this very perplexing problem.