What's done is done and I totally see the severity of you situation. Though, you can't un-watch the things you've seen. Work on accepting that with yourself and perhaps guide your self-forgiveness on, using some counter-actions?
Maybe make a donation to a child-protection organization like UNICEF? Do some volountary work with some children that need a happy moment or perhaps take an active part in your local community in making a more child-friendly environment?
I have tried doing some things to ease my mind of actions that I have done and it worked for me. What I've done can't be forgiven, but I still believe I can do good, based on what I've done. I'm a paying member in UNICEF and I'm doing some non-paid work for the local office in my town, this makes me feel better, maybe it would you too?
But remember, what you did is pretty much as 'innocent' as it gets, you should forgive yourself in the sense that you made a mistake and you have the option to try and atone for it, such that your paranoia disappears. It's not like you directly harmed anyone

Good luck buddy! I wish you all the best and I know you can fight through it all.
/inh
It may be that your whole purpose in life is simply to serve as a warning to others.