You need to be prepared for the fact that 90% if not more of your job is going to be safeguarding, you’ll have a case load of the most vulnerable children either due to ill physical or emotional health or unfortunate factors around their home circumstances - particularly those where the “toxic triad” is at play; parental mental illness, parental substance misuse or parental domestic abuse, or looked after children, etc.
It’s not a “Call the Midwife” type job of vaccinating healthy little people in the dining hall, these days. Unfortunately, and neither is health visiting.
I would read about The Healthy Child Program, ACES (adverse childhood experiences), absolutely brush up on your safeguarding knowledge and your understanding of the Children’s Act 1989, the Department of Educations “Working Together to Safeguard Children” which is statutory guidance, what your mandatory safeguarding/referral responsibilities are, I would look up all of the “Child Death/Serious Case Reviews” from the last 20 years (read the reports and look specifically at what role education/school nurses played in these cases and what they were asked to contribute to the review process) - Victoria Climbie particularly had lots of discussion of school in her review.
Go in with your eyes open, so many people go into SCPHN thinking it’s weighing babies and seeing happy new mums, and school nursing is vaccinating and bumped heads. - it’s absolutely nothing of the sort.
You can make a real difference to some of these children’s lives, but you will need resilience in bucketloads and very open eyes.