The 10yo probably weighed about that much - and humans of any age above infancy are capable of carrying their own weight, at least for short distances and if they are used to it. I know that from as early as I can remember, myself and my identical twin used to carry each other without any particular problem and without thinking it was out of the ordinary. Probably not a good idea for joints that are still developing, but that does not mean it was not done.
John

