The decision to buy a hard or soft mattress for an adult is one that can be made according to what is required of the mattress. It will depend on a wide variety of criteria. Some people have trouble sleeping on firmer mattresses and opt for a softer version. However, when it comes to children, it is recommended that a firm mattress is used. This is due to the effect that softer mattresses can have on the body. Softer mattresses can sink easier than a firm mattress and can thus cause the body to curve into an unnatural position due to the distribution of weight being heaviest in the middle 1/3 of the body. This can affect posture as a child grows and can cause damage as the child gets older. It is a big factor in proper spinal alignment as the child continues to grow. Firm support at this age can really save them with problems in the future.