Mani,
Your problem seems very "easy" to deal with.
The reason behind you are able to see the child company balance "0" can be as follows.
Reason : Your Fiscal Year and Period must be belong to the company for which you want to see the accounting balances.
Solution : If you want to see balances for Sub Company 1 then please select Fiscal Year and Periods for that company !
Fact : When Odoo calculates the balance from Account Move Lines, it filters the company & its fiscal period ids. If any mismatch in that, balance will be shown as "0"
For example, you select the Fiscal Year and Periods for Main Company and going to see COA balances for Sub Company 1, it will always 0. Just vacuum those values ( Fiscal Year and Months ) and try to see the balances. You will get what I am trying to explain.
I am sure this answer gonna be useful for you !