North Wales - base will be in Porthmadog

Borth-Y-Gest has a nice beach just SW of the village - but beware of going in the water due to tidal nature of estuary. Anyway, it is sheltered from most winds & south facing. (Borth-Y-Gest is right by Porthmadog). Nearby Portmeirion is unmissable.

I reckon that one of the best beaches in Britain is at Porth Dinllaen - which you can reach from Nefyn - which is also an excellent beach. These beaches face north & west so could be cool if the wind is from that direction. These beaches could be combined with a visit to Caernarvon Castle.

Bodnant Gardens - near Conway/Conwy are also well worth a visit - so combine these with Conway Castle and perhaps a look at the Victorian seaside resort of Llandudno.

I would also drive south - down the coast road to visit Harlech Castle. Then continue south to Barmouth = seaside town with harbour. From Barmouth, head east along the stunning Mawddach estuary towards Dolgellau before heading back to base via A470.

If you do visit Llandudno as James suggested you might want to take the tram up to the Great Orme Mine. I thought that was a very interesting visit to a prehistoric mine and it might be entertaining for the kids.

http://www.greatormemines.info/

Hi

If you are interested in old working trains in North Wales, you have an immense choice of lines to consider riding on; in fact, probably the widest choice of heritage lines in the whole UK. They are expensive for families, but worth it if you like that kind of thing (I do!). See 'Great Little Trains of Wales' web information as a point from which to do more research.

Any of the four famous Edwardian English Castles (Harlech; Conwy; Caernarfon; Beaumaris) are worth a visit, but the Welsh also built castles and, although far more ruinous, are just as historically interesting (Dolbadarn; Dolwyddelan). As mentioned by others, Great Orme Head, near Llandudno also contains a number of different attractions worth considering , and the views from it are good too. Sygun Copper Mine is worth a look if you don't want to see any more slate mines and, if you want to go inside a mountain and see a hydro-electric powerstation, visit 'Electric Mountain'. Lastly, for 5 to 8 year olds, the Anglesey Sea Zoo (across the Menai from Caernarfon) may please - just don't expect sea life like you see in Florida or California!

Just returned from Llandudno which was outstanding. There is plenty of hiking and the tram as mentioned previously. There is also a terrific pier with all sorts of fun things for kids and adults to do, you could spend a day between the pier/tram and the beach. The hop-on hop-off tour was fantastic, great way to see the area including town of Conway and the castle. The tour stops right at the Llandudno pier.