There's a reason why there is an age limit on alcohol consumption - it's toxic in large doses and can do damage to both the brain and liver.
We need to look at sugar in the same way, says professor Robert Lustig, and stop feeding our children sugar-filled breakfast that harms them:The Guardian: Sugar Is the 'Alcohol of the Child', Yet We Let It Dominate the Breakfast Table
It's wise to really start reading labels carefully to avoid unnecessary sugar, and remember that some common culprits are cereal, sweet yogurts and infant or toddler food.
Alternatively, just serve your child a real, homemade breakfast. Get some inspiration below.