There was a good outline of this in SAMM about 1 1/2 years ago.
If you are receiving renumeration for it, whether directly or indirectly, the law as it stands requires you to have the relevant NQF qualification, and be a registered guide with DEAT.
NQF qualifications are administed under the SAQA system. There are a couple of unit standards that may be appropriate:
1) Toprope supervisor
2) Single -pitch supervisor
3) Rock climbing guide (multi-pitch)
Of course if your activity involves a considerable walking component (ie not at a crag that's an easy jaunt from the road) then you will also require a unit standard called TG19 - mountain walking guide with limited scope.
If you are facilitating an activity on a volunteer basis, then this is not nessecary, but at least an MDT qualification is. The MDT syllabus is cery similar to that in the unit standards above, but avoids the beaurocracy / checks-and-balances associated with the NQF.
Particularly with children it's important to have your ducks in a row, as ultimately your 'clients' are not the children who partake the activity but their parents.
As with any such system there are pros and cons - with everyone bitching and moaning on each side, but that's the lie of the land. Welcome to pm me if you have any other questions.