You don't say what materials the floors and walls are make of.
If you are dealing with wood frame and gypsum board, I'd dispose of
them.
If you are dealing with concrete slab and block walls, a complete
drying and removal of paint or sealer, then refinishing might work.

If it is a single crack with no echoing crack, it might be the result
of shrinkage and not a worry.

In the end, it would be worth having a pro look at the conditions,
rather than taking the opinion of strangers.

TB