Hopefully the Spaniards might correct me but Reyes Magos is/was mainly to give gifts to children but now all people exchange gifts on this day, both old and young, similar (or same) to our Christmas day gift-opening rituals.

Yes, was just for childen

On the 6th of January TVE broadcasts a classical music concert from Vienna. Apart from that, I'm not sure. Normal broadcasting does not take place because few people are watching.

The tradition is the Vienna Philarmonic concert, 1st of January in the morning in RTVE

When we lived in Majadahonda, the family that lived next door always included us in their 3-Kings Day celebration and brought us a round cake with little toys baked in it. We would in turn, bring their kids halloween candy that we had bought from the U.S. Commisary down in Rota and bake them goodies at Christmas.