In reply to Steve Brooks:
How "nearby" the A5 can it be? - there are other areas in the Llanberis Pass and elsewhere. Are you looking for roadside, or is a walk-in OK?
Best areas (multiple routes in Diff-VS range; easy setups and fast resetting for next route etc) would include:
Trevor Quarry Quarry area. Not Snowdonia but 10 mins off the A5 on the way in/out of the Parc.
Craig Y Tonnau 20 mins off the A5 and a bit of a walk in but great rock, even if wet, and vertical pitches with good setups at the top. Juggy holds make it similar climbing to indoors walls.
Clogwyn Cyrau Little Buttress. Above Betws y coed, but quite a walk in whether you park at the bottom or the top. 15 short (10m) easy routes with massive trees/roots for belays at the top, great views over the town.
Creigiau Llynnau Mymbyr ('Ricks and racks') 2 minutes off the A5 at Capel curig, just past Plas y Brenin. Selection of nice routes in the right grade BUT toprope setups aren't always as easy as some routes wander a bit and finish out of sight of the base.
Craig Caseg Fraith Isaf Probably the best of the crags actually on the A5. Only downside is the £2 parking fee!
Idwall Quarry / Tin Can Alley Only a couple of lines here, but can be combined with Idwal Cottage Crag , which is bouldering but with some top-ropable lines, and if the kids are small/skinny they'll probably enjoy the Idwal Squeeze.
Most of these areas will need some trad gear and a static rope for setting the topropes.
Post edited at 21:40