The New York Times has a story about couples being driven from their beds by their young children. Apparently there is a thriving business in the upper middle class for "sleep consultants" who come up with conditioning regimes to get the little darlings to stay in their own princess and airplane fantasy beds. None of which the tired couples in the article found very helpful. Mostly, the parents report giving up fighting their kids for the big bed – the parents get used to going off to the children's beds in the middle of the night and sleeping there. One of the predictable effects of this strategy is that the couples do not have sex very often.
Faced with the same problem, Mrs. G. and I hit upon a different solution when our offspring were little, which is cheaper and lazier than the sleep consultant approach. For most of the pre-school years, we did not have an "up bed," but instead slept on a mattress on the floor. When the kids came in for comfort in the middle of the night, they would be content to sleep on the floor next to us, with only a few inches of elevation separating us. The inches were few, but precious: they meant the difference between a good night's sleep for mom and dad, and wearing nightly interruptions.
When the youngest was a reliable sleeper, everyone got up beds.
I don't know if this will work for you; I give it to you as free advice, and would welcome comparative stories.