That is the starting point unless your alleging that medical service providers are jumping straight to surgical options. My understanding is that transsexual only applies post-operatively - as such self diagnosis would be reserved to self indentification as transgender.
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Giving child legal right not to reveal whether M or F is meaningless (& likely damaging) because in reality their normal growth will make it clear. Also Q about whether it is ever appropriate to send child to school etc.. in a situation where they & others must lie about sex?
Anyway, point is, its a good question. You'd think @EHRC or @AmnestyUK or any of the other serious org would answer it in seriousness, instead of just mirroring whatever @Mermaids_Gender says