The UK is currently an ‘orange’ country for France. The French Gov website (https://www.diplomatie.gouv.fr/en/coming-to-france/coronavirus-advice-for-foreign-nationals-in-france/) makes this statement (11th June, 2021):
If you are vaccinated:
upon boarding, each traveller aged 11 years or older must present a negative PCR test taken less than 72 hours before the flight or a negative antigenic test taken less than 48 hours before the flight.
The measures regarding pressing grounds for travel and quarantine which are applicable to vaccinated adults also apply to any minors accompanying them, whether they are vaccinated or not.
If you are not vaccinated:
you can only travel to France if you have pressing grounds for travel. The list of pressing grounds is set out in the certificate of international travel drawn up by the Ministry of the Interior.
each traveller aged 11 years or older must present a negative PCR test taken less than 72 hours before departure or a negative antigenic test taken less than 48 hours before departure.
you may be subject to a random test when you arrive in France.
you must pledge to self-isolate for 7 days.