Well done. You obviously impressed them but someone just pipped you at the post.
I think a few of us have got jobs by being in the right place at the right time. I began volunteering, then doing my NVQ and was in the right place when another position came along. I then applied for another permanent position in the same school and the rest, as they say, is history. Even if nothing else comes along at least you will have relevant experience and a reference.
A few thoughts:
Is it enough hours (and pay) for now?
Is there anything else in the pipeline?
I would also want to know more about the child I would be working with before accepting the position.
Don't accept it because there is nothing else (at the moment) or in the hope of it leading to something more in the school. Hopefully it will but it may not and in most areas more jobs come up in September with the new intake.
Well done for getting this far and good luck whatever you decide to do.