If there's a question, err on the side of snugness. Avoid boards with too many cracks on the top surface. While surface cracks on skis aren't as detrimental, they can really cause the strength of the snowboard surface to deteriorate quickly. Don't buy it if there are raised bubbles on the base of the board made from the binding insert. That's what they are there for, to help.
Kids deserve the same consideration as adults.
They probably exercise and sweat more than an adult and need the same moisture wicking capabilities of the more expensive outdoor clothing. The problem is they change sizes and clothing more quickly than pro athletes change teams. Getting even a couple of years out of ski clothing for kids can be a major accomplishment. Here are some pointers for keeping things in check - honed from raising four skiers. High quality outdoor clothing will return years of service.