Listen man, children lack sexual orientation, because that part of their biology hasn't yet developed.
As I already pointed out, just because it isn't expressed doesn't mean it isn't already determined.
I am not going to entertain the ridiculous agnostic belief that it could be both, or one or the other.
Why is that so ridiculous when it's the consensus of the scientific community? Do you know better?
Unless you prove sexual orientation is latent and pre determined from birth. The null hypothesis is what i will go with here, until you prove otherwise.
It isn't a null hypothesis... Also I could easily say prove to me that sexual orientation is determined during puberty.
There is no link between sexual orientation and in utero development.
Literally just type it into Google. Apologies for Wikipedia as the source but:
There is evidence of a correlation between sexual orientation and traits that are determined in utero. Williams et al. (2000) found that finger length ratio, a characteristic controlled by prenatal hormones, is different in lesbians than in straight women. However, they found no difference between gay and straight men.  Another study by McFadden in 1998 found that auditory systems in the brain, another physical trait influenced by prenatal hormones is different in those of differing orientations; likewise the suprachiasmatic nucleus was found by Swaab and Hofman to be larger in homosexual men than in heterosexual men.
I don't need to prove anything, you do, for making that claim.
I have presented a viable alternative which if anything is more widely supported by current scientific consensus. Just because it's your view doesn't mean it can't be challenged...
I personally suspect it is a mixture of biological (genetic and prenatal 70%~) triggered by environmental factors, pressures etc. during early childhood (30%~). I'm not saying your suspicion is any more right or wrong than mine but I don't think the logic which has led you to that conclusion follows.