What should you do if you tickled a girl when you were 7?

I have been feeling awful about this for a long time. Back in the year 2000 I was 7 years old. I saw this little girl at a playground and she looked like she was 2 or 3. Out of nowhere I just started tickling her for no apparant reason. Her older brother and sister kept asking me to stop, but I continued. I did not know the girl and I never apologized and I have felt terrible about doing what I did. Should I continue to beat myself up over it, or should I move on?