J.M.
My son is 20 months and he still has his in his crib. He did the same thing with putting his head in the corner of his crib or sleeping funny up against the sides, and still does so I kept them in. They don't seem to be a safety hazard or anything for us. There was a point where he used them to stand on them and I thought that I would have to take them out, but now it doesn't seem to be and issue. I think it is ok to keep them in there as long as you don't notice him using them to try and get out of the crib or untie the strings, or some other thing where they may be dangerous.