New requirement for thailand. If you are traveling to Thailand with your child / children and only one of the parents are traveling you need to get letter from the other parent allowing the child to travel and this needs to stamped and signed by a lawyer with out this you are unable to travel. We got denied boarding yesterday on Air France.
TLDR : Answer Summary
Recent experiences indicate that flying to Thailand with a child requires a notarized letter of consent from the non-traveling parent if only one parent is present. Although some claim this is standard practice not newly enforced, others faced boarding issues with airlines like Air France due to this requirement. Commenters discuss varying enforcement levels and experiences in different countries regarding child travel consent.