"... it surely shows how much of an uphill struggle we've got when people who ride bikes in traffic are wary of campaigning for change by highlighting needless deaths because that's anti-motorist"
I'd agree with that. It's surely 'anti-child-death' rather than 'anti-motorist'?
In much the same way that drink drive campaigns are anti-drink-driving rather than anti-motorist. I still remember, as a kid, the public safety film with the kid throwing his frisbee into a sub-station. Never saw the ad as anti-frisbee, or anti-electricity. Simply highlight something that is dangerous and which is killing lots of people, and it might then get better.
The only problem I have with such things (and I can understand why it's done this way, cos kids are very emotive etc.) is it kind of suggests the life of an adult isn't as important to campaign about (though campaigns are not mutually exclusive of course, and if you make streets safe for children they should be even safer for adults who should have better road/common sense).
Using children in this way could be seen as cynical; but the Dutch have shown it's pretty damned effective. A politician is never going to want to come across as condoning killing kids.