>In forms one to many what is the best value to buffermodeoverride to child table and parent table (Optimistic table, optimitisc row)?
I use Optimistic Row Buffering for the parent, and Optimistic Table Buffering for the Child table.

>Where is the best method to do the data validation to rows? Valid? lostfocus? I have tried both but when the user decide revert
My forms use a save and cancel button to route all table updates or reversions.

Check your tastrade samples, and the MS knowledge base for ideas. What is "best" depends on what your system requirements are.