In addition to looking into possible illness and emotional issues as suggested already, do whatever you can to be sure your little guy is getting LOTS of physical exercise during the day. If you can convince his daycare provider to give him an hour or more outside, soaking up natural daylight, all the better. Just bundle him up well to protect from weather. This is not only relaxing to mind and muscle, but if he's restless because of toxins, it can help his body break them down.
Also, avoid TV or computer time within two hours of bed. Most of the light emitted from electronic screens is in the blue end of the spectrum, and this negatively affects the brain's production of melatonin, which helps induce normal sleep at night.
Finally, look at detoxifying his diet and environment. Try clearing his diet and sleeping area of all possible scented products,cleaners or other toxic chemicals, which can have a terrible impact on sleep and relaxation. Get a free and clear detergent and avoid fabric softeners entirely. You can add up to a cup of baking soda to the wash for extra cleaning, and a cup of white vinegar to the rinse cycle to soften his bedding and remove detergent residues (the pickle smell goes away by the time it's dry).
In his diet, avoid not only sugar, but all sources of caffeine (tea or many soft drinks), artificial colors and preservatives, all of which are proven to hype-up kids who are susceptible.
I have known children and adults (myself included) who have gotten much improved sleep with homeopathy, acupuncture, and even chiropractic adjustment.
Good luck. I hope you find answers that make a positive difference, quick.