M.B.
A.,
You make perfect sense here, and it will get worse before it gets better. On the brighter side though, it will be easier to change this NOW at 2 1/2 than at 7.
Super Nanny has two different techniques that will work. They have with my kids.
1st is for attached kids that need mom/dad in the room and it's a lot like what your pediatrician already suggested.
Sit on the floor cross legged with yourself in profile to your child. Sit with your hands folded in your lap, looking at the floor in front of you. Keep the room dim and **do not** interact with your little boy. Slowly, like once a week, or every few days move further away from your little boy and closer to the door until you're out the door.
The key to this one working is to not interact with them in any way. If they crawl into your lap or start trying to play with you gently put them back in bed and resume your position.
2nd is the one that works best with my kids.
1) do your normal bedtime routine (minus the laying in bed with him) and them give hugs and kisses and tuck him in bed.
2) The first time he gets out of bed give hugs and kisses and say "it's bed time sweetheart" and put him back in bed.
3) The second time he get up say "it's bed time sweetheart" and put him back in bed.
4) The third fourth and consecutive times say nothing and just put him back in bed.
This one works well on my daughter. Every night I have to put her to bed twice. The first time I do the full routine and the second time I pick her up by her arms, just under the armpit and lay her in bed, saying nothing. For some reason that gets the point across to her that Mom's not playing and the tantrum isn't gonna get her anywhere.
Sorry for the length and hope this helps,
Melissa