Hi -
I was in a similar situation, having only been a parent helper (father!), when I got my first TA job - but that was twenty years ago, and we were called Classroom Assistants then, and had less 'standing' than now. The other replies have told you most of the things you need to know; I would add that once you are settled, if you have any special skills - art, crafts, music, sport, cookery - let teachers know, and you might be able to support groups in you favourite activity!
As your teacher is NQT could be to your advantage, as she will look to you for support to some extent, and you can gain experience together! In my school TAs sat in on the weekly planning meeting with the teachers, so we knew what was going on even if we didn't influence things very much. Regarding discipline: my attitude is, Yes intervene in a tactful and unobtrusive way if you need to, but ask about that when you get there.
You may find this surprising, but the age of the children doesn't make all that much difference, other than the various levels of subject knowledge, life-skills, and general awareness and maturity. Children are children! My wife was an NNEB tutor at one time, and sometimes, after explaining in detail what was required, a teenage student would ask: Please Miss, what do we do? Just like in the 'baby' classes!
I had ten very happy years in an infant school, R, Yr1, Yr2,
and I sometimes also worked in the Nursery. I found I liked best whichever age group I was with at the time: nursery is lovely because the children give you cups of Plasticine 'tea'; with Yr2 children you can have more meaningful conversations, and help them understand Lit&Num concepts they might be struggling with. I once had a Yr6 child tell me she hadn't understood 'taking away' in Yr2 until I explained it to her. Adults use words that may be outside of a child's understanding and experience: 'Take Away' = where dad goes to get the 'Chinese' on Friday evening!
After ten years of KS1 I went to a secondary school for two years, and that was a 'culture shock', particularly as it was a notoriously tough school: when I said Good Morning on the way in, boys might tell me to 'F off'; other times they would offer me a cigarette (or worse!).
When I retired I continued to do voluntary work in schools, primary and secondary. A girl in Yr1 when I was first a 'parent helper' turned up again many years later in another school, on her final Teaching Practice year of teacher training! It was quite strange for both of us, but I told her to forget when she was six, and just use me in the classroom as she would any other adult assistant. (She is now a qualified and successful teacher.)
So: just relax and enjoy it, make sure the kids enjoy it, too, and I'm sure you will do very well.