A lot depends on how cold it gets and how big they are. I had seeds out all winter here in VA in 1 gallon containers. Last week I moved them inside and under the lights and have already had some sprout up. If you have them in a tray it wouldn’t hurt to just move them in the garage or even inside for an evening if possible.
Same here. Some plants can sprout up and survive a freeze but most can not here. Seeds in the ground even 1 inch down can still be viable come spring even with minus 30 degrees temperature but once they germinate and expose themselves above ground very few survive freezing temps just after germinating.