extra pay instead of holiday?? please help

[needhelpwiththis]

I work on an ad-hoc basis for an afterschool club. Hours depend on the number of children booked in for any particular day and can be anything from 6-20 per week.
I get paid hourly and some of the pay is holiday pay as we don't get any time off for holidays (the club is open in all the school holidays all day long as well as after school during term time).
Is that legal? How would my boss calculate that? I thought that every employee has to have 5.6 weeks holiday a year, but how is that worked out if (for example) I work 6 hours one week and 20 the next?
I want to make sure I'm getting everything I'm entitled to - can anyone help me?
TIA

They probably pro rata it into the your pay per hour, so you would have an actual salary payment per hour plus a holiday element per hour paid on top as your gross pay. They would work out what 5.6 weeks would be to a ft employee on same hourly salary and calculate that per hour (think it works out just over 10%). Perfectly legal if you employed on a sessional basis.

If you are casual or work irregular hours or shifts, there are calculations to work out how much holiday you get, have a read here.

However if you are working all year round every week, even if the number of hours varies each week, you must actually get time off.

What does your contract say?