Tricky call that Luke; it sounds like you've sussed the best venues already.
Maybe Caseg Fraith or Ogwen Cottage in the Ogwen - bit of a drive from Porthmadog though.
There is a bit of bouldering at Borth y Gest and Criccieth but it's nothing to get too excited about.
You might be better trading kiddy watching time with your missus and both of you nipping out on your own.
For a quick hit close to Porthmadog I would recommend seeking out Phil's Traverse 6B. It's an amazing rising traverse line on a huge ufo shaped block of dolerite stuck in the scree below Craig y Castell. A contender for the best of its grade in North Wales.
Thanks for the quick reply Si, I did go for a quick look for the Borth Y Gest/Criccieth bouldering once but gave up as I heard it wasn't anything to rave about.
Will check out that traverse soon, looks great! Really close to to the caravan too!
Forgetting easier problems (Girlfriend doesn't mind doing a bit of sunbathing instead) is there anywhere else you think would fit the bill?
I've just noticed some harder problems have been put up at the RAC boulders since your guide so I think I'll check them out!