I did once, after thinking I never would. I actually really got on well with the kid, I was just too young to a 'dad'. It was in Norway doing my Masters so I really only had 2-3 classes per day. Used to pick him up from school, sort his lunch, helped him with homework and played online games together. Just a shame the mother were a crazy crazy witch. She used to scratch her own face, hit herself and pull her own hair when we argued. I had to get out of there or get nicked. No cop would ever believe me.
This was back in the mid naughties. The kiddo got in touch last year. Somehow kept my email through the last 9 years. He's 21, married with a kid of his own. Made me feel very very very fucking old.