Check under any covers, in the tinies of spaces.
Could kitten or mum plus kitten in mouth have shot past you without noticing when you went in ?
If so extend to a whole house search.
Make the house really quiet, no diswasher, telly, close all windows and go around listening really hard.
If it makes you feel any better I lost a full sized cat from a closed bedroom when we moved here. We searched, extended to the house, assumed she must have slipped past and wandered out of thenhouse so conducted a field wide sesrch.
I went to bed in tears, only to pull back the covers and find her cowering there. She was well upset by the move and went super-hidey.
There was no perceptible bump, she was like pancaked under the duvet.
Agree with all of Cosie's suggestion.
She is the cat whisperer, and make suggestions well worth following.