How much should a 11 almost 12 year old charge for babysitting a 2 year old and 5 year old for 8 hrs you are certified in babysitting and first aid?

Depending on where you live, the usual rate is 5 dollars per child per hour. In your case you would actually be asking for 80 dollars. If the babysitting is happening during the day you may knock a little bit off the price, but it goes into the evening and the time goes past 10pm the hours after 10pm cost more because it's late.