How to explain to a young child about his erections?

Childhood Erections. You only need to provide as much information as is needed based on the age of the child. For a 4-5 year old, it would be sufficient to say that blood from the body goes into the penis in the morning and when the bladder is full caising it to be temporarily "straight"; "this is normal". More complete information can be added later when the child is old enouugh to process more complex ideas.