Won't stay down

Hardly a new problem, but certainly a consistent one with all our kids: the baby won't stay in bed.
When my wife decided he was big enough to be out of the crib, we got him this car bed (above). He liked it - as a toy - but preferred to sleep in our bed. No matter how many times we put him back in his own bed, no matter how often we told him how lucky he was to have such a nice bed, he still didn't want to sleep in it. So, one of us always ended up giving him our side of the bed, and my wife or I would end up on the couch.
So, I sent the car bed back to the store. Why pay so much for something he won't use? I got bunkbeds instead for the little girls. They love them, and neither of them has fallen off the top bunk.... yet.
The baby got a new toddler bed, not nearly as nice but just as unused. It's empty right now, while he's lying in our bed. Crosswise.
Wonder how we'll both fit on the couch...?