I don't know if the survey has space for free form text at the end for respondents to mention the poor wording of questions and the nature of them.
It might be a good opportunity for a parent to sit down with their child while filling in the survey and discuss the topics - why the questions are poorly designed, how to apply critical thinking to what's being asked, whether the question is misleading or inaccurate (to use your example of school uniforms being handled by local authority or individual schools), might it be a good idea to research a topic or proposed idea a bit further before answering based on emotions or because it simply sounds like a 'good' thing and so on.
I agree that a wider conversation needs to be had about the purpose and role of youth parliaments, how ideas are formed and policies proposed, how transparent the process actually is and whether there are strict guidelines around lobbying (the Denton's report makes it clear that trans and gender identity groups are targeting youth parliaments), and also if it is genuinely possible for young people to freely express contrary opinions and voice concerns / opposition on contentious topics.