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Their five-year marriage may be over, but Christina Aguilera and Jordan Bratman will always have one thing in common: their three-year-old son, Max.

The former spouses put on a united front when they came together Sunday to take their son trick-or-treating in L.A. Though Aguilera and Bratman kept it casual in civilian clothes, Max toughened up in a mediaeval soldier costume.

Since their October 2010 split, Aguilera, 30, says she and Bratman, 34, have been able to successfully co-parent Max with few disagreements.

"I definitely love the fact that Jordan and I are strong parents separated, and we both have such a strong role and a positive one in our son's life," Aguilera told Us Weekly in June. "We both share a special bond with Max. And that's a beautiful thing when he has both parents so involved in his life."