Would you believe that there is a really simple solution to this problem? Have you ever watched super nanny on one of the major networks? It's a show about a common parenting challenges solved by renowned "super nanny" Joe Frost. I have personally tried her methods and they work. First off, though in my own experience I find that my children go to bed without fail if I am very consistent with the bedtime routine. I have always used book reading (to them as they lay in their bed) as a reward for being cooperative while we bath, brush teeth and get into jammies. I also keep one step ahead of them by offering them a small drink (only like 1/4 cup of either water or milk) before they head to their rooms. They both have night lights and they always get big hugs and kisses before I leave their rooms.
Our routine goes something like this bath (on bath nights) or wash up (on alternative nights), brush teeth, get the small drink, put on jammies, go to the potty, read a book of their choice, (if they have been cooperative) and when I say cooperative, I mean that they have listened to my instructions and responded the first time I ask them to do something. If I have to ask twice, they are not cooperating. When they learn that you mean business about cooperating, bedtime routine will go like a breeze. Our routine sounds long, but from start to finish it takes about 30 minutes (a little longer if it's bath night as I let them take long baths). After they get read to I give them big hugs and kisses and them I bid them good night and leave the room. (A night light is helpful to some children) I have always taken the time to do this routine and whenever I try to cheat it, the results are not successful. I find that investing these 30 minutes pay off as I have rarely experienced the horrors that some parents describe with children popping out of their beds like popcorn. When my daughter transitioned to her big girl bed, she was curious about this newfound freedom. So I quickly responded with Joe Frost's suggestion which is: The first time they are up, you tell them it is bedtime and you walk them to their bed and tuck them back in and give a simple kiss and leave. 2nd time, you Say NOTHING and take them by the hand and tuck them back in, simple kiss and leave. 3rd time continue to SAY NOTHING, make less eye contact, refrain from trying to communicate through body language (don't let him know your annoyed beyond wit) put him back in bed (tucking in optional at this point) 4th time, Say nothing, walk him back (always walk him back instead of carry- the goal is to NOT give him anything kind of reward for his behavior) put him back in bed. 5th time, walk him back put him back in his bed ALWAYS SAYING NOTHING - BE EXPRESSIONLESS! No interaction. You will keep doing this without variation until he says put. This could take a long time to do the FIRST NIGHT... the second night will be less.... the third night will be even less... fourth night it should be cured... and always respond the same consistent way if the unwanted behavior should rear up a week or month later. If the method is followed without variation, it's a guaranteed cure! I would love to hear how it works out and my thanks go out to you and your husband for working so hard for our country.
Ok after reading some other replies, I have to add a couple of things. Sleep is very important. To take away a three year olds nap is only to create more problems. It is not healthy to deprive a child of a needed nap just so a parent gets a kid to collapse into bed at the end of the day. Go to www.sleeplady.com to read more about the importance of sleep and how much each age group requires. According to many sleep experts A child between the ages of 2-4 need 10.5 to 12.5 hours at night and one nap that is 1 to 3 hours long. It is not recommended to skip naps until a child is 5-6 years old! I always wonder if parents understand that sleep is just as important as food, if not more!
Next, locking a child in a room by locking their door with a hook is absurd. (and on some level abusive) my step mother took that approach with my half brother and let me just warn that the result was ugly and had a long lasting effect on my half brother.
The reply out "teaching" your child to stay in bed is great! Hopefully my step by step approach above will help you not to have to stay in the room with him. I have a lot of success with not having to stay in the room and I personally don't think staying is necessary. I reserve staying with my children in their room if they become frightened in the middle of the night by a storm or a scary dream.
My method outlined above will work at nap or bedtime. You can have a shortened routine at nap time. My children KNOW that after lunch comes nap. They don't even question it. First we have lunch, wash faces, go potty, wash hands, and I usually make sure what ever clothing they have on is comfy: example if my daughter has a dress on, I have her nap in her slip, or if my son has jeans on, I take the jeans off and just let him sleep in his undies... being comfortable is sometimes overlooked... anyways even at lunch you can read a short little book, maybe a board book at nap and a longer book at bed time. both of my children like to sleep with their lovies (teddy bear, baby doll) Hopefully your child has something that gives him some comfort... if not, you could go shopping with him and let him pick out a stuffed animal that he likes.
And lastly, I think telling a THREE year old that, "You are the big boy to help take care of us while Daddy is gone." is way to much pressure to put on a child who doesn't even comprehend fully why daddy is gone. He is a big boy, but not that to shoulder the weight of that statement! Heidi J's advise is great, but hmm.. I'd take the other's with a grain of salt. :)
Well, I know this is long, but I hope it helps. :) Best of luck to you and keep strong while your husband is abroad.