Is not telling one's parents about a trip before going on it considered disobedience to them, knowing that they were informed during the trip?

If the parents do not need the child for service or similar matters, he is permitted to travel safely without their permission, and this is not considered disobedience. It is, however, better to inform them out of filial piety. As for unsafe travel (such as travel for jihad that is not an individual obligation [ fard al-ayn ]), their permission is required. Any travel in which there is no guarantee of safety from perishing and in which the danger is severe is not permissible for the child to undertake without his parents' permission, due to the harm it would cause them. As for safe travel that does not cause them hardship, there is no objection to it. This also applies to travel for seeking knowledge if the path is safe.