Obviously you guys know your budget, but we have never taken more than about $200 dollars in cash in 10 years. Admitedly, we have only travelled with a max of 2 kids, but we have never taken travellers cheques either! You can use a credit card for just about anything, even small purchases so I would limit the amount of ready cash you take. In recent years We have used our debit cards and actually found that the exchange rate(which is good at the moment anyway), is even better. Think of what you might need cash for, ice creams on the move? Just about everything else can go on a credit card. Safer too.
All the best! Have a good one!
Carol