If you don't want to go through the menus, then I guess the best answer is bring 20% of your food allowance (assuming you are paying OOP)
If you budget $100/day for food, bring an extra $20 to cover gratuity. Some days you may tip more and others you may tip less. It should all work out.
If you are on a Dining Plan, then you'll also be tipping more. Having the extra food is great and can be a good value, but you can spend a lot more on tips. At a signature the average entree is about $40, but can be as high as $60, Desserts may be $10 or more, Appetizers can be $15, Beverage is $3, Adult Beverages can be $10. $88 per person, we'll estimate $90 to make sure you have enough. Your 3yo should be about $15. $195 - so budget a minimum of $39 per signature meal.
Regular TS meals can be as much $32 for the entree, $7 for dessert, $12 for appetizer, $3 for beverage, $10 for adult beverage. $64 per adult could be your average. Kids are $7.49. $136 - so budget a minimum of $27 for regular TS.