Yes, we used cot bumpers with all our 3 kids, and still do with the smallest (6 mths). They have loads of ties to keep them secure, and our babies tend to creep up the cot (not down) until their head gets wedged, rather uncomfortably, at the top or in a corner. The cot bumper at least keeps it a bit more comfortable!
Also our youngest has on occasion got a fist or foot stuck in the gaps at the end where the bumper didn't go around, so I got a larger one that goes all the way around. I think looking at the pattern is more stimulating for them (if awake in the cot) than looking thru jail-like bars!
Actually, the risk of suffocation never even occurred to me, I guess as we've always used all the ties and push the bottom edge into the mattress to make sure it's securely in place.
:lurking: