craftgrrl | Buttons for eyes on a baby toy?

Hi! I am going to knit up a few Socktopus ...(socktopi?) as gifts for my son and his friends, all of whom are babies around 6 months old who put every last thing in their mouths. If I were to use buttons for eyes, instead of embroidering them on, what would be the safest way to go about doing it? Really big buttons? Sew them on with fishing line? Or is it just a bad idea all around? I don't want them to be choking hazards, after all...

And so there's something crafty to look at:

I dyed this blue-faced leicester wool with kool-aid, cake dye, and food coloring, and then knit it up into these longies for my boy. For the life of me I can't photograph the colors properly, but the bluish color is actually a pretty good turquoise.