Sharing room for kids can be easy or can be not easy depending on the children and the arrangement of the room. If the kids have similar age, maybe they can easily share the room especially if they have been sharing a room since they were toddler. But if the different of the age is pretty huge, maybe we need to arrange the room so they can easily share.
If your kids have significant age different, it seems that you should provide a “private” space for each kid and probably some private toys, furniture and storage.
Also, if you want your baby sleeping in a room with his / her older sibling(s), a special attention should be made so the baby won’t get disturbed besides making arrangement to the kids bedroom. But here, at least you could find inspirations about designing a room for two or more children with different age.