An erection is when the penis becomes hard and stiff. It is caused by blood flowing into the tissue of the penis causing it to become thicker, longer and stiffer. When this blood flow stops the erection goes away. Boys can have erections from birth, but they happen more often during puberty.
Some erections can be caused by sexual arousal, while others can happen unexpectedly or when a person wakes up. This is normal.
It is important to teach your child about erections so they know what they are and what they should or should not do when they have one.