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One way you can repair and this might not be something you would even consider but it would clear your conscience is to talk to them about using drugs and the affect it can have on them and then tell them that you made some bad choice in your life where you experimented with drugs and it only bought you pain and embarrassment. If they are of age to hear about drugs that could be a way to make up for what you thought was betraying them but when they are children they really cannot tell that you were high or on drugs. I wouldn't feel too guilty about it and if you don't feel comfortable talking to them about drugs or don't think your brother would appreciate you doing so then you need to realize that you are only human and are going to make many more mistakes along the way. Make up your mind that from here and now that you are going to be the best role model they can have, use this as a way to start over with a clean slate.