Kids should get a new mattress about as often as adults, so every 6-8 years, or even 10 in some cases when the mattress is well-made and durable. If your child's mattress is showing signs of cracking or splitting in the foundation, that's also a sign you should replace their bed, no matter how long they've been resting on it for. Choosing a durable, supportive mattress can go a long way in terms of your child's quality of rest, which is why it's important to replace their bed when the time comes.