5 hour layover in Paris (CDG) while Bangkok-bound?

Unfortunately there just isn't time. While your parents luggage might be booked through, they will still need to get through Passport control at CDG and this is notoriously slow, sometimes one hour or more. Then they need to get to the RER train station and getting to an from Paris can take up to 45 mins each way. In addition, once in Paris, they need to make their way to wherever breakfast has been organised, and back to the station. Plus they need to be back at the airport at least 2 hours before their Bangkok flight departs. It's just not worth the worry.