11yr old DS has always been a problem sleeper, he's a worrier, easily scared and over active imagination so has always ended up in our bed at some point through the night, most nights. I haven't minded this too much as we co-slept with all 3 with no problems, expecting them to grow out of it as they got older. DD7 also wakes most nights and ends up in our bed too so it's often musical beds in our house as either DH or I move to one of their beds for more space and less disruption - they sleep perfectly in our bed but we don't now that they are bigger! Middle DC is the only one who stays in his own bed all night, every night.
In the last couple of months DD has started to go into DS's bed (he has a double bed) rather than come in to us. DS doesn't mind this at all, in fact he prefers it as he said he doesn't like sleeping alone. We're quite happy for DD to do this as it keeps them both out of our bed and it's quite sweet seeing the 2 of them cuddled up together. My only concern is that DS is 11 so on the verge of puberty and I'm wondering if it's appropriate for him to be sharing a bed with his little sister after a particular age? Should we discourage it or, again, assume that they will outgrow it soon enough?