In reply to Obi Wan:
Fun fact: the bouldering known as Porth Ysgo is actually at Porth Alwm. Porth Ysgo proper, just to the W, is a delightful little cove with a picturesque waterfall at the back, accessed by a nice set of NT funded wooden stairs. You can have a lovely family day here, it's great for swimming at high tide and rockpooling at low (we once found an octopus), and scramble round to Alwm for an hour bouldering. There is plenty of lowball stuff and the high easier stuff isn't really paddable anyway.
Another great option is Porth Oer aka Whistling Sands. Very nice sandy beach with cafe, nice for swimming, brilliant for kayaking, and at high tide often fun-sized clean waves for body-boarding. At the far (NE) end is a little sub-cove which has some fun bouldering at low tide, mostly above sand so good landings, but also fun caves etc to explore with kids.
Also recommend Porth Meudwy where the Enlli boat goes from, not done any proper bouldering here but there is some potential. Lovely swimming at high tide, deep clear water.
Walk up to the Coastguard lookout on Mynydd Mawr and down to St Mary's well. There are some short trad routes near here and we've done some semi-DWS/ cliff-jumping in the zawn on hot days.
The little Gabbro 'grit' crag of Mynydd Y Graig above Rhiw has nice rock but terrible landings. Better for easy solos, and on a good day probably the best view in Britain south of Loch Lomond.
On a wet day walk to the lifeboat station at Dinllaen via the pub, or if it's really grim go for brunch at Zinc in Abersoch.