I got this from the OFSTED website and point 6 seems to say you have to register if it involves money but not rewards (I would count as reward a nice box of choccies of some flowers). Reading it it seems less bonquers than I had previously thought :
""You do not have to register with us in the following cases.
1 If you care for children who are aged eight and over.
2 If you provide care where a child does not stay with you for more than two hours a day, even if your childcare service is open for longer than two hours.
3 If you only care for a child or children aged under eight who you are related to. A relative means a grandparent, aunt, uncle, brother or sister of a child (or half-brother or sister) or someone you are related to through marriage or civil partnership.
4 If you care for children aged under eight on domestic premises as a childminder without receiving any payment or reward for your services. Domestic premises can be your own home or someone else?s home.
5 If you are a foster carer for the children.
6 If you only care for the children of one or more friends in your own home or someone else?s home and no money changes hands, including money to pay for things like electricity and food.
7 If you provide care for children in their own home. This includes caring for children of up to two sets of parents completely or mainly in one or both sets of parents? homes. However, you need to register as a childminder if you look after the children of three sets of parents in any or all of the parents? homes.
8 If you only provide care between 6pm and 2am on domestic premises (babysitting arrangements). Domestic premises can be your own home or someone else?s home.
9 If you are providing a home-education arrangement where a child of school age receives full-time education outside school, and is partly or completely taught by a person other than a parent of the child. Care provided to the child is incidental to (not the main focus of) the education offered.
10 If you provide no more than two activities from the following list.
School study support or homework support
Sport
Performing arts
Arts and crafts
Religious, cultural or language study
This only applies if you care for children who are aged three and over, and you do not care for children aged under five for more than four hours in any one day. Any care provided is incidental (not the main focus of) to the provision.
11 If you provide care as part of your organisation?s activities in any of the following places.
A children?s home
A care home
A hospital in which a child is a patient
A residential family centre
A young offenders institution or secure training centre
12 If you are a school that provides education or care for children aged three and over, where at least one child being cared for is a pupil of the school. Children who are two years old when they start school but are three by the end of their first term at school (known as rising threes), may count as age three when deciding whether you need to register.
13 If you care for children under eight for four hours or less each day and the care is for the convenience of parents who plan to stay on the premises where you are providing care or within the immediate area. This type of provision has no long-term commitment to provide care for children ? for example, a shoppers? crèche, a crèche attached to a sports centre or adult learning centre, or an exhibition ? and covers services where children do not necessarily attend every day.
14 If you provide an open access scheme for children. An open access scheme allows children not in the early years age group (see note 1 below) to leave on their own. Childminders are not allowed to provide an open access scheme.
1 The early years age group is children aged from birth until the 31 August following their fifth birthday who go to early years settings that deliver the Early Years Foundation Stage.
15 If you care for children under eight from specific premises for 14 days or less in any year, and you let us know in writing at least 14 days before starting the service.
16 If you care for children between 6pm and 2am in hotels, guest houses or similar places. The care is for children of no more than two different clients, staying at the same place at the same time (babysitting arrangements).""