Gender dysphoria is rare, and cannot be accurately diagnosed or treated at age seven. I have medical training and I am fairly sure no reputable MHP would support this kind of parental intervention. It's one thing to have a boy who likes girl stuff and take that in stride. This is quite another thing. You don't become another sex at seven - you haven't even become fully your biological sex. Wait for puberty, see where that goes, then perhaps revisit the question - with a MHP being consulted.
It's like the old Jewish saying: have an open mind, but not so open your brain falls out.