Napping Hiatus

It's a phase right? At least that is what I keep telling myself. Alex has decided to give up napping. He's only two, so this has got to be a phase. I was under the impression that children needed naps up until at least the age of four. I have tried everything. He refuses to stay in his bed for even "quiet time". So I've come a a point now where I just don't know if I can keep forcing him to stay in there. It doesn't effect him though, if that is what you are thinking. He can go from morning to night without so much as an ounce of sleep and is just as happy at 10:00 in the morning as he is at 10:00 at night. Actually, he is crankier after a forced nap than he is without one. And to be honest, it's destroying poor Abby's sleep routine. She needs her sleep. And I do mean needs. She is a disaster if she doesn't get her 3 to 4 hours of daytime sleep. And now that they are sharing a bedroom (a joyful experience I hope to rectify one day with separate rooms), Abby just can't get sleep with Alex in there with her. He insists on keeping her awake. And the real trouble is that when she is sleeping soundly in her crib, Alex will go to take his 'nap' and will yell at the top of his lungs to entertain himself. He will then jump on Abby's crib railing and say "Abby, wake up!" This ends in the waking of Abby within moments and only leads to a very unhappy Abby. I'm not sure what has led to Alex's need to stay awake all day, but I'm starting to think he needs to have his brain stimulated more during the day. We already do playdough, markers, crayons, letter of the day, books, and dancing. He knows his alphabet and numbers for the most part, shapes, colors, and has mastered almost every puzzle we have in the house. What the heck else am I supposed to do with him for now? So unless I tie him to the bed kicking and screaming, it's either two frustrated children, or two happy children. I'm opting for the latter.