If they can spend more time where they are, until the weather starts to warm up, that would be what I would lean toward. It does take them time to fill out, feather in, and all that.
Last spring, when it was time for my runners to move into their own little house, I began taking them outside during the day into their day pen. Then once the nighttime temps were up to around 40, I gave them treats in their new house - peas! That, I hope, helped them associate good stuff with their house.
The night we had them out there for the first time, along came a wicked storm and knocked out the power. Yours truly went out there, flashlight and binky in tow, and spent a few hours with them in their 4'x8' house. When we all seemed to be settled down, I crept out the sliding door (2'x2' and down a ramp) and onto the sofa near the window near their place. Overprotective? Me??????
Eventually, I was convinced that they were okay out there predator-wise, and began sleeping in my own bed again.
It was when the night temperatures dropped to twenty several weeks ago that I saw that some of the ducks were not looking as well, were walking slowly, necks hunched back, feathers fluffed way out, and a couple of them were molting and shivering. What am I trying to prove by leaving them outside, for Pete's sake? We have the room in the basement (originally intended for ducks during hurricanes and high winds), so that is working out really well.
I have figured out how to manage their water and bedding with minimal mess. Now I just need to adjust the height of their basement pen so the cats can use the basement again. They are a bit disgruntled right now, the cats are. But they'll adjust.