My DS1 is 2 1/2 and we transferred him from his crib to his big boy bed (queen bed) about a month ago because he finally started jumping out of the crib. Since this transition he has stopped sleeping through the night and is up AT LEAST 3 times a night. He will not go to sleep unless you lay down with him. He is able to open his bedroom door so we installed an extra tall baby gate in his doorway so that he can't roam around the house in the middle of the night unattended. We had woken up several nights around 3 and 4 AM to him laying in bed with us, or playing in the living room in the pitch black, which prompted the baby gate installation. Since he has been in his big boy bed he wakes up screaming in terror and cannot put himself back to sleep without myself or my husband getting up and laying in his bed with him. We have a very strict nighttime schedule and he is in bed every night at 7:30. We follow the Bath, Milk, Book, Bed routine religiously and have not wavered from it in almost 2 years. We have tried the CIO method, checking on him in intervals of 5 minutes, allowing him to attempt to self soothe before we go reassure him everything is fine... nothing is working. He just stands at the baby gate screaming so loud that he is losing his voice. No one is getting any sleep including our 3 month old son and it seems to be getting worse each night. For the sake of our marriage my husband and I both refuse to sleep in his room with him, even though it would mean more and better sleep for everyone. We don't want it to turn into a bad habit. Help, what can we do to help him stay asleep at night? Its beginning to affect his attitude and his behavior at daycare... Any and all advice is welcome! TIA!!!

Losses:
7/16/2014 @ 7 Weeks 2 days
2/01/2015 @ 4 Weeks 4 days
Re: 2 1/2 YO with Sleep Issues
Other than just laying with him until he falls asleep & letting him fall asleep with you i have no other advice. This worked for us. Cant guarantee it will work for you. I hope you figure something out!
Keep me posted on how he's doing okay. Good luck!
My son is 16 months old so my advice may not apply but I'll toss in my 2 cents anyway.
I heard the easiest way to transition to a "big boy" bed is to take down the front railings of the crib and let him adjust to sleeping unconfined. That or get him a twin mattress. I think the queen sized bed may be too big for him and maybe he doesn't feel safe, which is why he's crying for you. Seeing the bars may have been comforting previously and since this is a big change for a little guy that may just be too much.
After my kid gets used to sleeping without bars I'm going to get him one of those awesome beds I always wanted as a kid myself (like a pirate ship or a car, whatever he's into when he's 2.5-3 years old). My hope is by making it fun maybe he'll want to stay in his room and not come into mine.
Disclaimer: I may be a bad source of advice because my 16 month old sleeps with my spouse and I
so we kind of fail in the sleep department but I'm a softy and don't mind sleeping with the boy most nights. We all sleep better this way anyway. I mean, he's not going to want to sleep with us forever. Babies eventually grow up!
Do you think you or DH could sleep with him in his room temporarily, as a transition? Give him some time to adjust to the new bed with the added comfort of a parent.
I also agree that a queen is awfully large for a 2 year old. I like the idea of letting him pick out a fun, child-size or twin bed. Or just let him pick out a fun blanket/sheet set, and/or some stuffed animals or pillows, get him involved and excited about his new bed.