1. Can we eat it. If the answer is no, we don't want it. Everything belongs in our mouths and if it can't easily make it in there (at least a corner of whatever it is) then we don't want it.
2. If I roll onto it in my awkward attempts to navigate the floor will it hurt my back/head/butt/legs/etc? If the answer is yes, don't buy it. Why punish me for my inability to control my body? It's frustrating enough as it is. Seriously.
3. If I flick it, smack it, shake it or roll it will it make noise or light up? If the answer is yes than buy it now. As a matter of fact, the more annoying the sounds and lights are to you the better.
4. As a side note to #3, when I shake it is it heavy or hard enough to hurt me when I inevitably bash myself in the head/face with it? If yes, drop it right now, it does not belong in that shopping basket. Do you know how humiliating it is to smack yourself in the face? It doesn't need to hurt as well.
And there you have it. If I come up with anything else, you'll be the first to know.
Sincerely,
Your infants. AKA: Your bosses
P.S. Also, buy two. I don't share well.