I've been to Costa Rica 4 times to surf and each time I've stayed in Tamarindo. Tamarindo beach is kid friendly and the waves are perfect for beginners. the Tamarindo area is chalk full of great waves and the vibe is very relaxed. The town is a bit more Americanized, however it is quite safe and full of good restaurants and places to chill.
Direct flights started from Denver to Liberia (about 45 minute drive to Tamarind) on Frontier in February.
Drop me a line if you need more information.