Unless you are a qualified mechanic you are treading on very dodgy ground insurance wise if you start making repairs on pupil's bikes. As a general rule of thumb, if you need to use a tool then it shouldn't be adjusted.
Nigel
DSA registered Driving Instructor, RoSPA Diploma in Advanced Car Instruction, SAFED registered van trainer, National Standards Cycling Instructor
IMHO, the biggest design fault on the majority of so-called kids' bikes is the shape and length of brake levers...why do they make 'em so small and impossible to reach with any force???