In reply to Inhambane:
The best option is Upper Tier at Tremadog, plenty of easy routes for children- I used to work for a centre that used the crag as its goto venue for beginners/ intro to climbing. The only downside is that there is a bit of a walk up hill to get there- however, with plenty of stops it's quite doable with kids. You can park on the high street/ road just off the high street on your way up to the crag.
Once you are there it also has great views across the bay with Portmadog and Penrhyndeudraeth.
Have fun
Craig Pant Ifan (Tremadog)
PS behind the main crag is a great little bouldering area suitable for beginners where you can also tunnel through/ under some of the boulders (if you are small)
Post edited at 09:12