In his book 'Celebration of discipline', Richard Foster takes us through a confession technique in the 'Confession' chapter. This will take over the next few days of the challenge.
Spend some time thinking over your past, specifically your childhood. There is likely to be things that you need forgiveness for that lie forgotten. Write down the things that come to mind in a list. Do not over think it, many things you will have asked for and received forgiveness already. God will make it clear what is still needed to be resolved.