Improved access to mental health treatment. We have free healthcare here, but the mental health side isn't great. This would also include support for those who are neurodivergant, suffering from trauma, experiencing gender dysphoria, etc..
Honestly, I think something that would be good as a policy is that at least once a year schoolchildren see a counsellor. Just to talk about anything that's bothering them, and give them help for things that are happening in their home life.