I don't know about 'sole' trader but if you are Ltd then it comes off your tax bill and you get a cheque back from HMRC.
The 6 week bit of it is calculated on your previous 3 months average income, so might be worth speaking with your accountant and paying yourself a bit extra for those 3 month's to make your 50% higher.
Double check all.that with your accountant incase its changed or you have other employees.
Sneeky one for you, to save running the nursery vouchers your business can pay the first £55 per week before tax, as long as the benefit is offered to all employees.