Many of Revit mEp families use a nested annotation symbol to provide the standard graphics we are used to seeing in electrical documentation. Here's a little example of a few of these families.
If you created a Callout view and these symbols vanish my bet is that you've used a Detail Callout. Here's what a Detail Callout view of the same families looks like.
It's definitely a quirky thing, but these nested annotations in outlets don't show up in Detail Callout view. Feel free to start trying adjustments to Visibility/Graphics, Detail Level, Discipline and more...I've been down the road already. I'm pretty sure we're looking at a bug, or at least a conundrum brought about by the way these nested annotations work.
This view type is also fussy about creating other elements, like a room/space for example. As such I understand that this view type is intended as the last stop or end of the road with regard to drafting up a detail, for detailing not modeling with. It's just odd that these annotation elements won't appear in the view.
If you want an enlarged plan to show these annotation then avoid the Detail Callout, use the Floor Plan type instead.