Hi bermannyc,
I’m not sure their reply answered why the description on their site says “granulated latex” but if the mattress contains 6" of Talalay latex that isn’t “granulated” (most likely blended talalay rather than 100% natural Talalay) and it’s in a medium or firmner firmness level then it would certainly make a suitable choice for a child.
They would be the most reliable source of information about the type and blend of latex they use in each of their mattresses. There is more about the different types and blends of latex in post #6 here but any type or blend of latex would be a durable material that would make a good choice for a child in a suitable firmness level.
I have known Mark and Dixie Foam for several years and they are also about to become one of the members of this site over the next few days which means that I think very highly of them and I believe that they compete well with the best in the industry in terns of their quality, value, service, and transparency. (UPDATE : They are now a member of this site as well)
Ventex makes inherent fire barriers that don’t have any added chemicals so I would consider them to be “safe enough” yes. All their mattresses (like all the mattresses that are legally sold in the US) have passed 1633 fire regulations so they are also an effective fire barrier.
Phoenix