Philips HX6042/33 Sonicare Kids 7+ -varaharja, 2 kpl

My 8 year old is very petite and the brush head for 7+yrs is too big for her mouth/teeth, (resulting in them not being cleaned effectively) but the smaller head for4-6yrs isn't firm enough for her adult teeth. It would be great if we could purchase the firmer bristles with a smaller head.

I have the whole range of heads, and I like the colours, which makes it much easier to know it belongs to the kids, but can see no advantage, size wise to a standard head.