Postcard in local shop/newsagents window.
I would suggest putting on it details of what you want the person to do, as the time period is short and I expect you want them to do something specific, such as take your dd to school.
I've seen ads in the local paper for mother's helps - you could try that.
I've paid £10 for 1 hour (8am to 9am) in the past for someone to play with ds after breakfast then walk him to school.
Also try gumtree (free ads) there are local boards on there and maybe netmums? - also have local childcare boards.
>What do I do about CRB checks.
As a parent employing a private carer, at present you can't get a CRB check done on your employee.
Therefore, if you require that they have a CRB check, state that in your advertisement, and rely on the last check they had - ideally it should be less than a year old, though could be up to 3 years old. Suggest not accepting one older than 3 years.