To make as much good Kamma as you can right now to balance the negative Kamma that you did at that time. I don't know whether Steve has mentioned about the salt in the water, has he? Negative Kamma is a bit like you have half a cup of hot water and you dump half a cup of salt into the water and you stir it up. Most people don't want to drink that. However, if you pour that salty water into a bathtub and then add buckets and buckets and buckets of clear water until it is full, then the salty water gets diluted and you can drink that water. There is not much you can do to take out that salt, but you can dilute it by being generous. So focus on making good Kamma now and develop the Generosity Parami is a way you can make up for past unbeneficial actions.
I don't think there is any benefit in talking with your parents about stealing from them as a young teenager. Dealing with this past bad Kamma is an internal process, unless you feel like you could be more generous towards your parents. Consider how you have changed and that you are not that little kid any more, you are not a teenager any more, wanting money and stealing. Reflect upon how that it is something that you never want to do again.
Reflect on the Dukkha that comes from taking what is not given in relation to the Truthfulness Parami. By reflecting on the Dukkha of unbeneficial actions helps us to not repeat that action. But certainly making lots of good Kamma, being generous, especially focusing on the Generosity and Truthfulness Parami can help in making good Kamma here and now. Reflect on the person you were then and the person you are now to see how you have changed. Another way to help is to do the D/D method, the diffusing, universalizing technique to understand that it is not just you but many teenagers who may have stolen from their parents and they like you have the capacity to change.