Sometimes saying "goodnight" to kids can go on for a while as you call goodnight many times while walking down the hallway!!! And then of course they may re-appear and the process starts again! Be firm but caring and it will be nicer for everyone.
Beds are meant to be clean, safe and warm. Warm in the sense of temperature if it is winter and in terms of a warm and loving place to sleep.
It is nice to think of different ways to say goodnight but if it is just a kiss on the cheek and the word goodnight, then that is perfectly fine too.
Some other words I like that are related to sleep and that could be used in a goodnight text or in person:
2. sweet dreams
And sometimes words are not even necessary, but a hug and smile will do the trick.
My daughter was asking me the other night how to get to sleep because she was having trouble. I told her not to try too hard, but to notice things about her while she rests. I told her to listen to her breathing, and feel her fingers on her legs and to feel her toes. I mentioned some examples that would keep her in the present moment and allow her mind to relax and drift off to sleep as her eye-lashes hugged!