My requirement is once I Estimate the BOM A then automatically Bom B, C, D, are need to estimate but due to change in site in between production, remaining BOM production order is not creating automatically from site change.
The estimate will not do this if I understand what you are saying, you probably need to look at pegged supply and planning to drive and connect all of the elements. With teh pegged supply you can then estimate all together, but it depends what you really require it to do.
But in my case , once I estimate the Production order then in pegging, child Production order will create up to same site but if change in site within chain of BOM then remaining orders will not create.
No you do not need to create the production order manually, these are referenced production orders created at the same time as the parent production order. If you configure the BOM to pull items from a separate warehouse it would naturally cascade this down the chain. Have you actually set this up - if you have can you describe your level 0 and level 1 setup, the orders produced and what you feel it should do against what it is doing.
No you would not be able to do this manually from memory, item C that comes from site 2 would need to be transferred, you could setup pegged consumption but your issue is with the related cross site setup. Your C is made at site 2 which means it needs to be consumed from there but cannot in a site 1 BOM. Planning could work, manually I think not, but you would need to set it up and see I am afraid.