The situation: a five month old baby is put down for a nap in the middle of a double bed, in a bedroom, and left unsupervised (door closed), but parents check in every so often (realistically every 3-5 minutes or so). The baby is placed in the middle of the bed. The duvet is folded down, away from the baby, a loose blanket is placed on the baby, from chest down. Two pillows are placed on either side of the baby, at the side edges of bed, in case baby rolls off bed.
YABU - this is fine, I would be happy with this situation
YANBU - this isn’t OK, I wouldn’t do this.