Moss,
The problems with stones in Cumbria (and probably Derbyshire, Yorkshire, Scotland, and any other walkink/climbing areas) is that very reason: adults and children pull them apart. In some cases the cairn is moved substantially, or reduced into a small pile, covering a greater area. Who's to say if there's a burial, or if that burial is diturbed. Sometimes the centre of the cairn is cleared to the ground. Then the tread of feet uncovers the top soil - then what?
It's all part of the same problem - especially with non-excavated cairns, which are subject to educated guesswork as to what they contain.
Regards,
TE.