MDIChild change other MDIChild objects

Question

Hello:
 
Is there a simple way to have a MDIChild change any object in a different MDIChild.
 
I think in C++Builder there was an "#include" that gives you the option to change any object in the other form.
 
(*Again: I am a super newbie and I hope I explained this correctly. I should probably use this as my signature...lol)