There are a few issues here.
(1) The readabilitly of type at a certain point size, especially small sizes, depends primarily on the typeface you select. 5 point Helvetica (a fairly plain sans serif face) is much easier to read than 5 point Bodoni. Italic or oblique styles are much harder to read at smaller point sizes.
(2) With text at small sizes, be careful about what color you print. The most legible would be 100% black with no other colors. Once you get involve with any tints or combination of colors, you have to deal with the visual results of halftoning and even more so, registration of inks. If you are reverse printing, i.e. white on a background color, make sure that you use a bold style or else your text may be illegible and the darker the background color, the better.
(3) The product may be for a younger crowd, but you should not assume that all young people have perfect vision. I know plenty of younger people wearing bifocal and trifocal lens glasses. And if the information you need to print is critical to proper use of the product, making difficult to read for persons who don't have excellent vision can expose you to legal problems.
This sounds a little crazy, but what I would do is to take your design, printed at the final size, and give it to some older people, especially some obviously wearing glasses, and ask them about readibility of your design. Better yet, produce a few samples with different typefaces and styles and see the reactions.
'Tis all I needed to know. Thanks Sir!