Dogwatch
1 - 600€ is £495 - see
Currency Converter | OANDA very naughty to try to stiff you on the FX rate
2 - Cash the cheque, write a letter thanking the tour operator for their kind service recovery gesture, which you accept without prejudice to your EU rights and then go after TCX for the 600€ - an ex gratia payment from the tour operator does not cancel your son's rights