The best evidence supports DNA being the main culprit in being a crossdresser or transgender.

MRI studies confirm the transgender brain is very different from a hetero and gay brain and the evidence would indicate nature as causal vs nurture since the studies include 18 - 50+ yr old TG participants and all TG age groups show the same differences vis a vis hetero and gay brains age groups and the results have been replicated.

Google " Transgender MRI Studies" - fascinating stuff...

FWIW - I think if mothers were asked they would id the TG child easily from birth by the different disposition of the infant vs her other kids.