I love adding fabric covered buttons to my projects. They can always go sweet and girly or funky and modern, but they're also great for boys since masculine trims and decorations are so limited. Buttons can add that little something extra and still be boyish. They're a great way to give new life to an old garment, adding them to a coat or cardigan is an easy upgrade and can give that sort of "vintagey/Anthropologie" feel that I'm crazy about (notice next time you go shopping how many really nice garments have fabric covered buttons).
I always use the Dritz brand, half-ball cover buttons, these are 3/4" size ($2.99 for 4). They are really easy to assemble without any tools and are very sturdy and secure after assembly, but you do have the option of prying off the backing if you make a mistake or need to change fabrics. The ones that require a tool cannot be undone. These can be thrown in the washer and dryer and come in many different sizes.
Purchase your buttons, when you open it up you'll find an equal number of curved front pieces and flat back pieces. Raid the scrap bag and cut rounds just a little larger on all sides than the button. (There is a template and some brief instructions on the back of the Dritz box.). One thing that I always do is sandwich a small circle of interfacing approximately the same size as the button between the button and fabric. The metal is so shiny that after stretching the fabric around the cover, it can still reflect through-even if it's not sheer. This takes away from the quality, something akin to wearing a flimsy dress without a slip. :)
Next use your thumbs to pull the fabric up and over the edges of the cover, catching it on the spikes. Once it is relatively smooth and evenly distributed, grab the button backing and pop it on. Easy peasy...
And with rewarding results!