I've found starting with the "...when they're ready to go without training wheels, try removing the pedals and dropping the saddle..."
tactic is received well. Then, gauge it from there if I start spruiking balance bikes. It's generally helped do that latter when I've had one of my two on one at the time. I'd imagine I only have a few weeks of that yet - I can't see her taking it to her first day in Prep.