Mine all went through a HotRock, and had no issues transitioning to ‘normal’ brakes – youngest started on the 16″ at 3 and has moved to a 20″ Hotrock with dual Vs at 5 without even a murmur.

You can also do MASSIVE skids on a coaster brake for some years after you’ve technically outgrown it.

Not being able to backpedal is a PITA when they throw the chain and you have to fix it with no tools mind.

Or the 16″ form the new Raleigh Performance range – £200 and 6.48kg

ridgeback mx16 are a tough and not heavy for a kids bike..

I never asked but again it never seemed to be an issue. Stopping them launching themselves off inappropriate stuff, different question.
The front calliper is again perfectly adequate for the slightly digital nature of a 3 year olds braking, they don’t really do modulation, so not having it possible to lock on hard works quite well.

Ups are bloody hard work on child gearing. And a Gatorbar towed child with a coaster brake will find it immensely amusing to lock it on when you’re towing them up to the top of the woods. You may not after the 321351 time.

Talking about brakes my 4 year old has actually had front v-brake only since just before he was 3. He can go down steeps and stop suddenly with no problems – the key is to get them standing on their pedals.

The Hotrock is heavy – the 12 inch version is 7.5kg so 16 is heavier. Would be a great bike if it had v-brakes instead of the coaster.

Pics I found had calliper front – hunting again I’ve found pics of the 2015 models with and without a front brake. I guess it probably depends on where they’re being sold.