I've just bought my first bike in 20 years - a 29" mountain bike. And, inevitably, I've just got my first puncture in 20 years, and a lot has changed. The first thing I noticed is that today's bikes all now use the car-type valve. When I tried pumping the tyres with an "el cheapo" football pump, no way could I get air into it. Had to buy a car-type pump.
Now that I've bought a valve insert removal tool, the reason is obvious. The spring that closes the valve is so strong that pump pressure cannot open it: it's necessary to use the clamp-on adaptor that seizes the valve thread and pulls a pin into the valve to hold it open against the spring.
If memory serves, the old push-bike valves used a simple rubber sleeve over the insert that acted as a one-way valve when pump pressure was applied.
Are these still available, or are there "softer" valve inserts available that make pumping tyres easier for kids to do without having to understand the reason for the clamp-on adaptor?