The bike shop I used to work for sold a lot of child helmets (as we specialized in “alternative transport” as opposed to sporty bikes) and I always found Abus helmets to be the best.
The band on the back comes down very low, so once they’re fitted they’re very secure.
Also, the straps are routed through the band at the back, so they dont move around much and, once fitted, they sit well clear of your child’s ears.
As the main band is sort of floating, it generally fits well to pretty much any shape of head. The problem I always found with Met, Giro etc is that the band doesn’t do this, so the fit was never as secure. They’re also dead easy to fit.
They do a massive range of sizes, colours, and many of them have a wee light in the back (although your kid’s probably not going to be riding on the road, it’s a nice thing to have for peace of mind, and kids love to play with them!)
Well worth a look, in my opinion.