Appeals question

[RonTberry]

I'm a Cal Ripken 9-12 coach. My first post here so I apologize if this has been covered.

In a recent game I felt a runner left early from 3B on a caught fly ball. After play ended and ball returned to my pitcher I called time so my pitcher couldn't throw a pitch and instructed my third baseman to go to bag and for my pitcher to throw it to him for the appeal. The umpire told me I could not appeal because my calling timeout to tell my kids how to do it killed the appeal. He said once a TO was called no appeal could be made. I've searched the rule book but can't find any confirmation. Would appreciate being pointed to the section that states this if it is the rule. Thanks in advance.