I think that's a pretty normal attachment and a pretty normal "growing out of it".
Evan, in his infinite quirkiness, has a special ball.
He always prefers a ball to most other toys, but this one, in particular, is his favorite.
He carries it around constantly.
He eats with it.
He sleeps with it.
After he falls asleep at night, we laugh when we hear the ball hit the floor and go rolling away. When he wakes up, it's the first thing that he wants. Sometimes it falls in the crack and we have to fish it out for him.
When it rolls away during play and gets lost for a while (like it has been for the last couple days), he will sometimes replace it with something else-- a small, blue, bottle cap, for example. But he remembers his ball and cries for it at bedtime and is always glad to see it again when it turns up.
It's so funny to me that he chose this particular ball to be so attached to. I have tried offering another ball of similar size, but he won't have anything to do with it. He only wants this one, hard, plastic ball.
...it has a sad face on it.
...just like him.