nah, you would have scared them an i doubt they will do it again. some guy drove past me on a narrow country lane in a ferrari yesterday and revved his engine REALLY loud just as he passed. it gave me a little shock but then i just thought that he's probably compensating for something with a jackass car/attitude like that. kids wont read into it that much, if that was me when i was 15 and most of the lads i hung around with we would have been scared despite the laughing afterwards (thats just what kids do) and would not do it again. you didnt hurt them you just scared them, its cool imho