ok, if i can add my two cents
I agree with several posters saying that it all depends on the context of the scene. With the turtles' scenes, the teens werent tickled on their feet for a sexual reason, but only for drive them crazy enough to give up the jewel (or diamond or whatever, its been years)
another example I thought of is the clip of the children getting their feet tickled for an experiment for bbc uk online. While some may take it in a sexual context, it was originaly created purposely for the experimentation of the nerve endings in bare soles.
It's kinda the same with female bondage and the whole damsel in distress scenario. With TV and movies, it is not really meant to be a sexual situation (again, talking about kids cartoons/series stuff) but there to express danger or trapping (if again, in TMNT, if the Shredder ties up April O Neil, that is the universal sign that she is in danger) If a person becomes fond of that situation, that is totally unpredictable. To be honest, I still dont know what triggered my tickle/foot fetishes, but before I could remember, I loved tying bare feet, watching them flex, and tickling them to make them do moreso. I mean, is a 11yrd tickling the barefeet of a 11yrd girl playfully, to see what make her tick, the same of as 21yrd old doing the same thing, of course it isnt.
In the end, we, as adults, should be able to judge what is morally right and wrong. After all, arent the two kids in the TMNT voiced by people in their 30s? At the same time, this should also draw the line between this stuff and that of the scenario above, which I'm refering to tyflas and pinderloy messing around with 3yr old and such.