The reason why your child counts is because over the years, restaurants have changed their financial metrics when reporting to stock holders. It used to just be all about sales vs previous year and budget, but now they have metrics in which guests served vs. check average , guest per labor hour spent, and food cost per guest, so they have taken the stance of if you breathe, you are a guest. If your child doesn't order anything off of the menu, only eats the cherios that you brought them, then they are still a guest, because the restaurant has to use labor hours in cleaning up after them and they have to justify all of their hours when it comes to budgeting. Like many things when it comes to financials in a buisness, they can't pick and choose which metrics they are going to use so the only way to have consistent financial data is to include all. They have all chosen to create a blanket rule to be consistent, the thing that tears down restaurants quicker than anything is inconsistency in product or service, and if you have different rules for different guests, people will stop coming in.
If you want to blame something.....blame capitalism....if companies weren't so freaking greedy, then we could actually go to a system where higher wages were paid to servers, and tips would not be necessary. There are a few restaurants in the Pittsburgh area where they are testing this, they are paying their servers a salary, giving them better health benefits and stock options, so that the servers are more invested in the success of the company and thus care more about taking better care of the guests, as well as not looking to move to the new restaurant that moves in down the street because the grass looks greener.