Possible to restrict block creation outside of parent?

We have some simple blocks that make up various lists and grids. Each parent list/grid block accepts any number of child blocks of specific types to render output. Using the child blocks outside of the parent listing context does not make sense and we'd prefer to prevent an editor from even selecting those types of child blocks outside of editing the parent block. Is this possible?

Example:

Parent List Block
 - Child List Item
 - Child List Item
 - Child List item

Editor should not be able to make a standalone Child List Item, and we'd prefer those not show up in block type selection unless they are creating a new block from inside the Parent List Block's content area.

Any direction on this is appreciated - and if there's a suggestion on a different pattern to accomplish this type of thing, we are receptive to that as well.

Thanks!