We have one that has openings so it can be used on the seats for tiny babies as well as the regular trolley seats. We still use it now even though Sam is 18 months old. There's a few reasons for it - Sam seems to like leaning over and chomping on the trolley and I don't want him damaging his teeth on the trolley! What might happen if we hit a bump while he's biting on the trolley is something I just don't want to think about. He doesn't do it when the cover is on. Also, the one time I put him in a trolley without it, I found the straps on the trolley itself couldn't be adjusted to hold him in properly. Our cover has it's own straps - it velcros onto the trolley and then has it's own straps to hold him in. He's much more secure that way and can't climb out as he tries to do when he's just in the trolley without it. I'm going to continue to use it for as long as necessary, for us it's not necessarily about germs, it's about his physical safety as well. And the pockets in it for other things are really useful too!

BW