When you think about bedding I am sure you think of bedding, so now I think parents will choose to purchase king size bed because they can sleep with their children. Other than that king size bed against the wall is good because if children sleeping inside against the wall, you not need to worry that he or she will fell down from bed.
Many people think that Queen Size bed is not but think of it, children do grow fast and you don't forget about both parents sleeping on the same bed. You will need more space so choose bed that is suitable for the family and loved one.
So now even though you think that you have a single bed in the room but it is not enough because you need to buy the bed rail for the bed if the children sleeping in. Just in case you worry he or she will fall down from bed.
I think King Size bed with Single Bed are perfect! Parents can sleep in the king size bed and children sleep on the single bed.