I can't really help on what they 'should' be able to do as my y6 DD struggles. But certainly by the end of y5 they would have been introduced to fractions, percentages and written methods for division and multiplication.
If you are going to 'help' then you need to make sure you know the methods the school uses. Number lines going on to different written methods.
Here are my general tips for helping with maths (maths degree but 2 children who don't find academics easy). In no particular order.
You need to start with what they can do and start from there. It won't help their confidence to have you throw things at them that they can't do.
So start with open questions:
- have you been taught about percentages
- what can you tell me about them
Do you know what 1/2 means.
etc.
When doing methods for e.g. multiplication and division, use 'easy' numbers like 2 and 5 and 3, that they know their times tables for. So not 262/8 but 685/5.
When doing adding and subtracting, I find using coins helpful and the concept of 'going to the bank' to exchange 10ps for 10x1p or whatever useful for introducing column methods.
Fractions can usefully be done with talking about dividing pizzas. Haven't found a good practical method for showing how to multiply and divide them though.
Do they know about the fingers trick for the 9x table.
All the above is for 'basic' numeracy.
There is more emphasis on wordy problems these days too. Picking out the numbers from within the words and working out what to do with them.
RUCESAC (Read, Underline, Choose, Estimate, Solve, Answer, Check)
Hope this helps.