Just a though on keeping track of a child's allowance; make them accountable for it to get it each week.
Teach your child about receipts and writing down what you spend your money on, then tell your child that they have to show you at the end of each week where they spent their allowance in order to get it again next week.
Say they get $10 a week allowance, and at the end of the week they only have receipts for $5 in spending (they can only account for half of the money they spent). So they only get $5 allowance the next week.
If they can account for it all each week, then give them their full allowance, and maybe give them a dollar extra if they save some money during the week as incentive to save money.
