Hi chrstnamarie,
You can see the specifics of the Roma here. As you can see it’s a finished two sided mattress with a tape edged (non zip) cover.
The 6" special is a component latex mattress which allows you to choose the firmness of each layer (and side to side as well in a queen size or larger) and comes with an unquilted cotton stretchy knit cover which can be unzipped to give you access to the latex layers inside (similar to the Spindle Mattress). Component mattresses allow you to change the firmness level of either of the layers and you can also replace the layers down the road as well without having to replace the whole mattress.
The Spindle mattress is also a component latex mattress which uses a slightly different version of Dunlop latex (continuous pour rather than made in a mold) and has a wool quilted cover.
Yes this would be the layering I would generally suggest for kids because their body is less developed and “curvy” and they don’t tend to need softer layers to keep them in their best alignment but with lighter children a “relatively” soft layer (not extra soft) would also be suitable because with the supportive nature of latex they would be unlikely to have any support/alignment issues. As a general rule (and of course generic guidelines don’t apply to any specific kids) girls tend to prefer slightly softer mattresses than boys. A softer top layer may also be a preference choice for parents that spend more time with their kids on the mattress.
Phoenix