tubular tires with sealant would be a nice setup if you have an old set of training wheels. Something like a conti gatorskin 25 would be good. the clincher version of that tire is too slow to race on though.

my understanding is the latex tubes help reduce the pinch flat tendency in clinchers but I have no first hand experience with them

Shame you can't mooch a cross bike off someone and just run a 28 size clincher at 85 psi