The best children’s cycling helmet is with innovative MIPS technology. Cycling helmet with MIPS.

What is MIPS? MIPS stands for Multi-Directional Impact Protection System.
If you fall on your head, your brain can literally slosh back and forth in your skull. MIPS helps to reduce that.
MIPS is an extra layer inside your bicycle helmet. That layer can rotate slightly apart from your bike helmet, at the moment that your bicycle helmet collides with something
The outer layer of the bicycle helmet catches the big bang. MIPS then ensures that your head can move a little bit inside the bicycle helmet or the bicycle helmet moves a little bit with the object / ground you are colliding with. MIPS reduces the impact and thus reduces the risk of a brain injury.
Website with clarifying images and information: http://mipsprotection.com/technology/
Children’s bicycle helmets of the brand GIRO are also equipped with MIPS technology. All models are available with and without MIPS.