Thanks for the nice feedback. I'll admit that I spent the whole day shooting this, as well as my daughter biking alongside of me, and some photos would be more / better blurred, but this one was just too good to pass up; after all, it captures the essence of my kids - my always scared daughter and my son who can't get enough of anything
As for your question - I wasn't going too fast, maybe 25 km/h, which I guess in the eyes of the little ones can be a lot. It's a 1/5s exposure.
Excellent shot, both in technical merit and content! Your picture gave me a smile.
They seem to be close in size, are your kids twins? I have a pair of boy/girl twins who turn 8 in August and I remember the bike-trailer days. They've since graduated to the "tag-a-long" bikes and now onto their own 6-speed mountain bikes (I'm an avid mountain biker).
They are 2 and 4, exactly 2 years apart (which makes birthday parties a bit of a challenge). But the little guy is quite huge for his age, so they seem closer than they are.