Do you mean $100 per person per day? If so, that's rather high unless you plan on doing TS meals.
At CS, it's approximately $12-$15 pp, including drink. Kids approx. $8. Churros, popcorn, soda, etc are all approx. $3 each. So if you're eating 2 CS meals (2x15=30) plus get a few snacks/drinks (let's say 5x3=15), then you'd be spending approx. $45 on food per day on the adults. You can easily spend less than that if money is tight or if you don't snack as much, bring your own drinks/snacks into the park, split meals, etc.
How much you spend on souvenirs could really depend on what you have in mind. I mean you can go from $.50 to as much as you want to spend. We tend to not buy much there b/c frankly (IMO) you can get the same stuff elsewhere for almost 1/2 or even less than 1/2 the price. (ie- got my girls play Mickey cellphones for $6. at the Emporium. Saw the exact same ones as Walmart when we got back for $2.75) If it didn't specifically say "
Disneyland" on it, we usually won't buy it. We personally limited our daughters (ages 3.5 & 5) last time we went to just $20 each for the entire trip (we bought their snacks and drinks). We knew that they'd ask for everything and it'd just end up at the bottom of the toy box a week later. We used it as a learning experience and didn't budge from their total. It was rather interesting to see how they'd change their mind on what to get when they realized that they wouldn't have anymore money left to get something else. Anyway, obviously you can spend as little or as much on souvenirs as you'd want. I'd personally save all the shopping for your last day. That way you know how much extra $$ you have and don't risk running low (and having to worry about carrying/storing everything) on funds part way through your vacation.
Bottom line? You could easily do WAY less than $100pdpp, especially for your 3yo. Or you could easily do more.
Depends on your eating habits and spending.