New Austrailian Shepard not adjusting?

I've adopted a 1year old male heeler, and I'm not sure how it's working out. I've had a heeler before, and she was a ball of energy, playful. But Ollie here, he just lounges around, has no interest in a ball or bone. He will foloow us from room to room, but turns skittish if we make a sudden movement in his direction. He has no interest in going outdoors. He is loveable as can be, but a total foot dog. He was intended as a pal for our 3 year old, but he has no playfulness! His former owner said this was just his temperment, and would tkae him back if it didn't work out. Should I give him back and opt for a dog with more vigor before my son gets too attached, or ride it out for a few months and hope he'll perk up?