In
Knitting for Baby (Melanie Falick and Kristin Nicholas, 2002), there's a pattern for "Baby's First Ball." The balls can be stuffed with "4 large handfuls of clean, raw wool, or wool yarn scraps, or 2 large handfuls of polyester fiberfill per ball."
The balls are stitched, felted, stuffed, and then closed up, so the stuffing has very little chance of poking through.
DCM