I found this great pattern for a fun, "3D" ball for babies; even my toddler likes playing with them! I've made several in bright colours but I've only got one posted on Etsy so far!
The balls are great for tummy time because they'll roll, but not TOO far since they're not really "round". They're also great because they're soft enough to be thrown around IN the house (if Mama will allow such things!).
Let me know what you think!