There are various level 2 or 3 qualifications you can take, usually involving at least one day a week in a school. Most jobs seem to be advertised at level 2, but you can get a level 1 job without any qualifications if you have experience. I started my job at level 1, no TA qualifications but I had experience volunteering in the DC's preschool.
It is a great job, very rewarding and the hours can fit in very nicely with your own DC if you are in the same school or nearby. But be warned, nobody does it for the pay, which is awful. Also, depending on the school, you may be expected to plan your own sessions for working with specific children, or deliver specific interventions with targets- it is a lot more than just a bit of photocopying and hearing children read (which is all some people seem to think it is!) .
The hours etc really vary- be aware that anything from 25 to 30 hours could end up being full time school hours, depending on whether you are paid for breaks/lunch hour. In our school the specific working hours are negotiated with the class teacher, then approved (or not) by the head. Eg I start at 8.15 each day so that I can leave at 3.15 to pick up the DC.
In our school you may move year groups sometimes, but will nearly always stay within either KS1 or KS2.
It was a massive career change for me and the lowest paid job I've ever had, but I love it!