Cancer is rare in children, but it's common in adults, meaning that many kids are affected by it - even if they're not ill themselves.
One of those kids is 11-year-old Charlie, whose dad was diagnosed with cancer.
Charlie's father had to go into hospital for nine months. When he came out, he couldn't do simple things like turn on the TV or go swimming.
But a year ago, Charlie found out the good news that his dad's treatment had worked. Watch the clip for his story.
Watch Newsround's special, Living with Cancer, on Tuesday 29th March, 4:55pm, CBBC on BBC One.