Do you have the original image i.e. was this image scanned from paper or scanned from a color negative or positive?
The reason I ask is that one of the key limiters to the image is that the image is scanned at too low of a resolution and in addition the image has very highly compressed when stored in the JPEG format. By setting the scanning resolution much higher and using a high quality compression setting with the JPEG format, you would have a much better shot at having a higher quality result.
If you don't have that ability, only marginal improvement will be able to be achieved. So thought I would ask if you have a better or opportunity to get a better image file to share first.
I completely agree with John that a bigger scan would get much better results.
Have you tried asking at a local library - certainly in this country (UK) many libraries will give you access to a decent scanner.
Even your scanner should have the facility to save the file in a variety of formats - don't choose .jpg go for something like .bmp then you will at least get an image that has a better chance of enlarging.
Here is a cropped version of your image trying to make it look as good as I can given the limitations of the original image. Not much sharpening helped, yet I took out some of the JPEG file artifacts, increased the clarity, adjusted the white balance, cropped, and cloned out some distractors
Just to show why it is so hard to fix, the resolution is very very low. Not that in this side by side comparison (original on left, adjusted on the right), The eye of the boy is only 3 pixels wide and 3 pixels high. There is not detail from which to work and improve. Just wanted to provide some more information on why having a better original would be key to higher quality.
So to answer specifically about marginal improvement. The one element that can be removed is the pixelated look. By upsizing with specific rendering algorithms and using adding a blur and then resizing, you can get rid of the pixel edges. So that looks better yet it is not really sharpened.
So that is why having the best possible original is critical in getting a much better image. Photoshop magic is limited by the quality of the original image supplied. Hope the extra details help explain this a bit better. Note that this is what the eye does automatically when viewing the larger image from a distance or just not enlarging the image quite as much.