Is it permissible to use a child’s car seat found next to a charity collection bin, or must it be returned to the charity, and is it considered a type of "luqata" (found property)?

Your husband is not permitted to take the chair he found next to the charity collection bin designated for donations. This is because the owners of such items intend them as charity for the poor, and it is not considered a lost-and-found item. Rather, he must return to the charity organization and seek their permission to take it. If they grant him permission, then there is no objection.