Do jaw expanding braces really work in stopping snoring in children?

Maybe. There is not a definitive link in the literature yet, but many parents have reported this to me as well for kids undergoing expansion. Snoring is adolescents often is induced by a constricted upper airway via swelling of the adenoids and/or reduced nasal space. Palatal expansion indirectly affects the airway and could improve the issue. I would also have an ENT evaluation for your child.
It could. If upper jaw matches width of lower jaw, do not do expansion. If upper jaw narrow, expansion will increase airway and may help. Have ENT check tonsils and adenoids. Have orthodontist (such as dr peter pfaffenbach in schenectady--your home town) check transverse jaw relationships.
Jaw Surgery Snoring. In children, the best way to help relieve snoring is removing the tonsils and adenoids. This will help most. I often also perform surgery to reduce swelling of the turbinates, if stuffy nose is also present. Jaw expansion may be helpful in children under age ~8 years, if there is a high-arched palate. Moving the lower jaw or upper jaw forward to expand the airway may be helpful. See an ent/orthodo.
In some yes. In some patients these can be very helpful. You have to find out if the jaw is still forming by seeing orthodontist familiar with this. There is defnitely age when this can help. After teen years, not helpeful.