Your DC will be fine. Depending on the size of the school, there are probably parallel classes in the same year group and their teachers will share planning and resources and advise where needed.
The people talking about not much work happening in the last couple of weeks before Christmas are right to an extent, but I know that most of that, in previous years, may be due to Christmas plays which take up huge swathes of time in rehearsals. They won't be happening this year, so I would assume that maths and English will be carrying on a usual with maybe more Christmassy activities in the afternoons. It is all learning. Doing arts and crafts is still learning!
The fact that schools can't afford supply teachers is the real scandal. It's a scandal for the children, for the TAs, who would be teachers if that's what they really wanted to be, and for the thousands of supply teachers, who are ready and willing and getting no work coming their way.
This is the result of underfunding in schools, which has been going on for years and which people need to be more aware of and campaigning about.
Your DC will be fine. Nearly every TA I have ever worked with has been utterly tremendous. They know the school and the children and have heaps of experience. They will have seen hundreds of teachers - good, bad and indifferent - and will have learned so much about how to get the best out of the pupils. The school will have thought hard about how competent that particular TA is and I have no doubt they will manage brilliantly.
It is not fair on the TA, though. It is a different job with different pressures. I am going to hope that all of the extra assessments and paperwork that are required at the end of a term are not going to land on them, but wouldn't be at al surprised if they were suddenly expected to do all of the extra admin too. It isn't their job. It's not fair.
Everyone is having to be flexible at the moment - including parents. Try to support the school and your own DC. They will be fine, though. They will not stop learning.