There is hardly any administration required after the initial setup. If you go to the trouble to run your limited, run your own voucher scheme. It's really simple. Everything you need is here -
http://www.hmrc.gov.uk/childcare/
Just design a poster / memo advertising the scheme (I did mine in Word in 30 minutes) and state it must be available to all employees of MyCo. I googled what an example childcare voucher looked like and designed my own in Word. Monthly administration consists of printing off a voucher, and signing it, childcarer countersigns it and returns it to me. £243 is paid directly to her account from MyLtdCo. All you have to do to meet the obligations of the scheme is to make a note of their OFSTED registration number and when it expires.
If you are within the weekly £55 or monthly £243 limits it does not have to be reported on the P11d either (only if it's for more than this). The voucher amount makes up part of your remuneration and is used to reduce YourLtdCo Corp Tax bill.