How to charge when battery already dead
The Kidizoom is a camera, not a battery charger. If you wan to use rechargeable batteries, you'll have to charge those batteries in a separate, appropriate charger.
If by "dead" you mean a broken, defective, or past end of life battery, then there is nothing you can do to charge it again. If you simply mean a completely drained battery, put it into an appropriate charger and charge it following the instructions for that charger.
NEVER try to charge a non-rechargeable battery.