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Film, Media & TV5 mins ago
No best answer has yet been selected by fatcat. Once a best answer has been selected, it will be shown here.
For more on marking an answer as the "Best Answer", please visit our FAQ.As BossyBoots says, as far as the UK Government is concerned, a child under 16 can travel on this type of passport until the expiration date at which time the child must have its own passport.
http://www.ukpa.gov.uk/_1_applications/1_babies.asp
I cannot categorically confirm as to whether the French will accept this as a valid passport, however since they still issue adult passports with children placed on them I would tend to think that they will.