Douglas knew that he fucked up as soon as the identical soulmarks appeared on the skin of the trio. A celtic ailm symbol, presumably a symbol of Adam's strength; a lightning bolt, the definitely obvious symbol of Bree's speed; and a knot of Isis, presumably to symbol Chase's intended wisdom and intelligence in his chips.
Douglas wasn't stupid. He knew that he was playing god by creating the trio. But he didn't think that it would have resulted in the trio being soulmates to each other.
They were just kids, Adam only three, Bree almost two, and Chase was six months old. They were too young to know what the symbols would mean, or become to mean as they got older.