When you say it needs to be plated, do you mean it should be able to take ballistic plate inserts? Because the vest you linked can't do that. Tactical Tailor MAV's and Mini MAV's are adjustable down to 5 year old sizes, but they also can't take a plate.
This is a good compromise, it will adjust down to a very small size and can hold a plate.
http://www.tacticaltailor.com/modularplatecarrier.aspx
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