Once again, a reminder: Children are unpredictable. Marine Capt. Greg Wagner and his wife, Meredith, saw that firsthand on Christmas as President Obama visited Marine Corps Base Hawaii. While the couple took a photograph with the president, their 8-month-old son, Cooper, put his hand in Obama’s mouth. Meredith said this morning on Good Morning America that she was “mortified” at the time, even though it appears that Obama laughed it all off. “I was mortified,” she said. “I was embarrassed.” Capt. Wagner gave the president credit for keeping things light. “He kind of laughed and said that Cooper looked up…