Back in the 70's it was common place for children (like myself back then) to be cared for by neighbours/friends for part of the day, to give my own parents a break.
I am not sure when Registered Childminding first started... does anyone know? I know it was in the \link{http://www.opsi.gov.uk/ACTS/acts1989/Ukpga_19890041_en_1.htm/Children Act 1989}, but it may well have been included in Acts prior to that, such as The Nurseries and Child-Minders Regulation Act 1948, The Child Care Act 1980. Anyway, history isn't really important to answer your question, though knowing why regulation was introduced could help you understand the legal position regarding caring for someone else's child.
Latest Legislation is Childcare Act 2006
The Meaning of 'Childcare' is defined in the Childcare Act 2006 differently to how it was in the past. I would suggest you read Section 18 - Meaning of Childcare .
So I highly expect that you would fall under the act in terms of providing 'Childcare'.
Next stage is to establish what a Early Years Childminder is. This is defined in Section 96 of Childcare Act 2006.
From the ACT
(4) Subject to subsection (5), "early years childminding" means early years provision on domestic premises for reward (and "early years childminder" is to be read accordingly).
(5) Early years provision on domestic premises for reward is not early years childminding if at any time the number of persons providing the early years provision on the premises or assisting with the provision exceeds three.
End of quote from ACT
The important bit there is FOR REWARD. Reward does not mean money. While it often is money, it can include other things, such as a bunch of flowers, box of chocolate, exchange in some sort of service.
In your particular case, the payment of £24 is REWARD in my view.
One thing you have not mentioned is the age of the child. I will presume that the child is aged 5 years or under.
Currently to get around the issue of needing to become a Registered Childminder, you will need to care for the child in the child's own home, as a nanny. Nannies are now included in the Childcare Act 2006, but do not have to register.
For those asking about Babysitting. Babysitting is the same as Nannying, it is childcare provided in the child's own home. Therefore currently it is exempt from registration.
If a childminder were to care for children at their home in the evening (6pm to 2am) then under the Care Standards Act 2000, childminding provided between 6pm and 2am is exempt from registration. See section 79A paragraph 8. Overnight care however needs to be registered - as that would include care after 2am.
IMPORTANT: I am not a lawyer, I am a childcare provider. The above is my understanding of the legislation as it applies to those in England. Please seek professional legal advise if you feel you need it.