They already said quite clearly that they're transphobic. The "I don't think children should undergo gender or sex transition" is almost verbatim an anti-trans talking point.
Here's some actual research on the subject of trans people, including trans youth, and suicide risk. With citations;
Bauer, et al., 2015: Transition vastly reduces risks of suicide attempts, and the farther along in transition someone is the lower that risk gets.
de Vries, et al, 2014: A clinical protocol of a multidisciplinary team with mental health professionals, physicians, and surgeons, including puberty suppression, followed by cross-sex hormones and gender reassignment surgery, provides trans youth the opportunity to develop into well-functioning young adults. All showed significant improvement in their psychological health, and they had notably lower rates of internalizing psychopathology than previously reported among trans children living as their natal sex. Well-being was similar to or better than same-age young adults from the general population.
Gorton, 2011 (Prepared for the San Francisco Department of Public Health): “In a cross-sectional study of 141 transgender patients, Kuiper and Cohen-Kittenis found that after medical intervention and treatments, suicide fell from 19 percent to zero percent in transgender men and from 24 percent to 6 percent in transgender women.)”
Murad, et al., 2010: "Significant decrease in suicidality post-treatment. The average reduction was from 30% pretreatment to 8% post treatment."
De Cuypere, et al., 2006: Rate of suicide attempts dropped dramatically from 29.3% to 5.1% after receiving medical and surgical treatment among Dutch patients treated from 1986-2001.
UK study: "Suicidal ideation and actual attempts reduced after transition, with 63% thinking about or attempting suicide more before they transitioned and only 3% thinking about or attempting suicide more post-transition.
Heylens, 2014: Found that the psychological state of transgender people "resembled those of a general population after hormone therapy was initiated."
Perez-Brumer, 2017: "These findings suggest that interventions that address depression and school-based victimization could decrease gender identity-based disparities in suicidal ideation."
Here's a study showing that children know what gender they prefer and don't change their minds on it.