When I am creating a Rem reference on a rem with existing children, the children do not go into the newly created Rem reference. My suggestion is when you select a block (parent Rem + children) and type [, everything gets moved over to the new reference. This way, I don’t have to manually move the children to the reference.
Sure you aren’t confusing references with portals? Sounds like you’d be better served by copying and pasting in a portal. In fact, you can quickly paste in a portal from any reference by ctrl+clicking it or right clicking and selecting “insert into document”.