Hi Edy Simon,
I can help you. For making a Sales BOM an Item should be only Sale Item not an Inventory Item or Purchase Item.
Lets I01 is a Sale Item & I02 and I03 are its child. Child Item can be anything type. Make a Sales BOM using I01.
Now select I01 on Sales Quotation or Sales Order you will get the Child item too after selecting the I01.
Thanks
Ankit Chauhan