Childcare vouchers are just another type of deduction.
They should reconcile with the purchases
So it would make sense to give them a control account, post the purchase of vouchers and the payroll deductions to that account and make sure everything zeros out.
The payroll deduction would just be part of your payroll journal and the purchase of vouchers is... an invoice from your supplier, a bank payment or whatever it is in your case.
If you are using Sage Payroll, you could get the payroll to pop it in a separate nominal.
If you use a standard Sage nominal structure the control account should be somewhere around 2240
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