Well done on getting an interview. TA jobs can be like gold dust, especially if you have limited experience or relevant qualifications. Having your own child in the school shouldn't be a problem; many of our TAs do. Be ready for questions on how you would manage it. i.e. how you would respond if your child misbehaves or gets told off by the teacher in front of you, how you would deal with pupil fall outs involving your child and how you would respond to pupils' parents with your different "hats" on. Tell them you will explain your different roles to your DC and expect them to treat you more like staff than mummy in school.
You don't mention what year group the role is for so interview questions and expectations are very different. Wear something smart, but that the interviewer could envisage you actually doing the job in.
As far as the interview goes be ready to work with a group of children - be careful not to over direct them (this is something we find many parents and less experiences TAs do) and try not to do things for them, support them in doing it for themselves.
I suggest you look at the school's safeguarding / child protection policies. If they are not available without you going in to collect one try googling safeguarding policy primary school and your county to find one that would probably be similar. You will get interview questions about safeguarding and even if you don't know the answers if you have shown initiative and researched you would get mega brownie points from me. You will be given induction training including safeguarding, but when we ask "what do you know about safeguarding in schools and what your responsibility would be?" it can freeze some people.
You may be asked how flexible you can be regarding additional cover hours, school day trips, extra dinner time support if the TA hours are part time. Have you thought about child care? Our TAs start work 20 mins before the dorrs open and stay an additional 20 minutes after end of school. Who would care for your DC if that is the same at your school? It does really depend on the school's policy, but you can't really drop off in reception as the doors open and be ready to start your job at the start of the day as well. I really like it when candidates have already thought of that and have arrangements in place. same goes for additional meetings and training after school or on PD days. Also what about when your child is ill? We don't give unlimited leave to care for sick children as it impacts the care of the children in school.
Finally express an interest in additional training and qualifications, but don't voice you are planning on starting a PGCE next year (some did in my last set of interviews - why should we train someone who will be gone in a year?)
TAs do an amazing job and we couldn't function without you! Let your love of children and desire to help them shine through at the interview and show your own personality (it is so important as the role is so based on relationships). GOOD LUCK!