What will they be using them for?
You have basically 2 figures.
e.g. 8 x 42
8 is magnification level and 42 is the lens diametre.
Don't assume that higher power is better as there are a lot of trade offs. Also consider weight. Heavy if you're carrying it around your neck all day.
Loads of info here.
http://www.binocularscanada.com/faqs.asp