How Do I Get My 2Yo to Stay in Bed and Nap Again?

This is a new thing for your son, so it will take a little transition time. When I moved my daughter to a toddler bed at 21 months, she too, resisted a nap and wanted to play instead. After a few days of playing instead of napping, I set up the pack and play in her room at nap time and I gave her the choice which bed she wanted to sleep in. Most of the time, she would choose her "travel bed" and took a good nap.
At bedtime, I didn't offer her the choice and always put her down in the toddler bed. For a couple of weeks, she would play for a while and would often fall asleep in the floor, so we would just move her to her bed when we checked on her later. After a few weeks of getting used to the bed at nighttime, she began wanting to sleep in her "big girl bed" for naps too. We're now a couple months in and I no longer give her the pack and play option and she naps as well as she did in her crib.
I think giving her a little control over her nap helped her. I also think allowing her time to get used to the bed at night helped because she's always been better about nighttime sleep than she is about naps.
Do what works for you and your son and good luck! Let us know how it works out.

If he stays in his room and plays quietly I'd just let that happen. This is a new thing and he'll adjust to nap time in bed again. However, if he comes out of his room or get's boistrous then I'd calmly put him back in bed each time he gets out. I'd do this without fuss. Just calmly put him back in bed and tell him it's nap time.

If he's just getting out of bed to quietly play on the floor you may find that after a few times of doing that, and if you stay out of the room, that he'll fall asleep on the floor. this is OK. He's getting the rest that he needs.

Do not make being in a bed a big deal. If you do it can easily turn into a battle of wills.

I went through that times two recently. My girls are 15 months apart. My 3 yr old at the time 2 was very difficult and still is. I just have to be diligent and make her lay down. Also if your son goes to a nursery school, one of the tricks me and my husband finally caught on to is to play music. Now I lay my girls down for their nap and turn on the classical music channel. I make sure that she is laying down and within 10 or so minutes she and her baby sister are snoozing away. Hopefully it will work for awhile. Good luck because I know how it is to have a cranky toddler.

I had this same problem with my daughter. What I ended up doing was to remove anything from her room that was of interest to her and at a level that she could reach - books, stuffed animals, etc. and then put babyproofing locks on her drawers and cabinets. It was a bit of work to do all of this, but after weeks of trying the "silent return to bed" method over and over again with zero success, that's what we had to do. She's now napping for two hours at a time every day, no problem. Just hang in there and don't give up on the nap. Two year olds also go through a phase where they try to drop their nap even though they still really need it. Good luck!