Try VCHEK saliva for kidsAgreed on the Hough - quite a few complaints on my local forums that the torch didn't work or battery was flat.
But the reality is most people take what they can get.
Most kid friendly I found was Orawell. Instructions are to cough into a tissue. Then only mouth scrape. But then you have to keep the scope under your tongue for up to 2min to get enough saliva into the unit to take the fluid past the control line.
nice big lollipop to swab mouth is easy to use and V high sens