One of my grandchildren comes from a household where the parents could completely darken the children's room and they did so at bedtime. That works great with poultry – when the light is gone, they are calm – but it didn’t work with grandchildren. He stood smiling in his crib in the morning as if he had smelled the light. His successor slept significantly lighter; in my opinion, a difference in sleep behavior was rather related to the respective condition.
Hotels have blackout curtains, it doesn’t cost a fortune and no light comes through the fabric at all. Anyone who can sew can make them with manageable effort. I would, for example, look at stoffe.de.
Wishing you restful nights with or without light protection!
Gabriele