Hi Rupesh, I'll explain this with a simple example this will related if you have three files or twenty files.
I have a directory with the part files 'bolt.prt', 'nut.prt' and 'washer.prt' if I want to know which is the parent and which is the child open any part, I chose to open the nut.prt, the procedure is as follows:
From the menu bar goto Assemblies > Reports > Where used
The 'Where used Report' dialogue box opens, choose 'Enter Directory' and browse to the directory you have all your part files in.
In my case I'm pointing to H:\Temp\UG directory\ which has the parts I'm querying. Hit 'OK'
A 'Where used Report' pops up showing that one 'nut' is used in the 'bolt' part which tells me the 'bolt.prt' is the parent and 'nut.prt' is the child.
Now that we've established that 'bolt.prt' is the parent of an assembly, we open that part with the following load options so it can find all other child parts.
From the menu bar goto File > Options > Assembly Load Options
Select 'From folder' option and hit 'OK'
Open part and I choose 'bolt.prt'
And there you have it! the assembly opens, 'bolt.prt' is the parent and 'nut.prt' along with 'washer.prt' are the children.