Although every child is different, according to Home Food Safety
a general rule of thumb is a child is old enough to use a microwave
when he can read food preparation instructions on a package and understand a microwave's keypad. Instant oatmeal is a good first meal to allow your child to make when using the microwave on his own, and also makes a filling breakfast. He can add some peanut butter, dried fruit, nuts, or seeds for a little added texture.
Always discuss microwave safety before allowing your child to use it on his own — use this printable microwave safety sheet for kids to make sure you cover everything.
If you have time for a little make-ahead prep, baked oatmeal squares are a great substitute for instant oatmeal and are perfect for mornings your child may need to eat his breakfast on the run. Make and cut a batch using your own healthy recipe, or try this one, and store in an air-tight container for easy grabbing.