Being mindful of calories per dollar goes hand in hand with knowing how many calories per person per day you need.
Generally, an active adult needs "between 2000-2600 calories per day, more if very active. Children need 1500-1600 calories per day to maintain growth and energy" (See 14 Tips for Food Storage Shopping). So taking the calories you need per day and multiplying it by 365 days in a year, an adult would need between 730,000-949,000 calories in one year. A child would need between 547,500-584,000 calories in one year.
Also remember that most food storage will store at least 10 years, and some for as long as 25 years (for more information on shelf life, please see Tip #13) . In 10 years your 9 year old will be in college, and in 25 he/she could have kids of their own. Be ready to add to your supply for your kids as they grow or plan for them as adults, depending on your circumstances. It's always better to have a little extra than not enough.