Uwila has a great list of questions which you can use as a starting point. You may need to modify them slightly to fit with your specific requirements, but it should give you a good starting point.
Uwila's Nanny / Au-Pair Questionaire
Having a CRB check done can be tricky for both the nanny and the parent employing the nanny. If you are recruiting a nanny via an agency, the nanny should have a CRB check done via that agency, within the first month of being in your employment. Upon joining the agency, they may have started the process of obtaining a CRB check, so may have this already by the time you interview them. Nannies may also have CRB checks from pervious years, these can be useful, though it is important that once they have started in your job, that a new CRB check is applied for.
If you are not using an agency, and the nanny is also not registered with an agency, then there is no current way of getting a CRB check done, except under the Approved Nanny (Childcare Approval Scheme).
You could ask for an APPROVED NANNY. Nannies who are APPROVED have a CRB check done annually as part of their ongoing approval. A benefit of having an APPROVED NANNY is that if your employer provides Childcare Vouchers, or if you are getting Childcare Tax Credit, you can pay part of your nannies wages using these schemes. NOTE: Approved Nannies are only available in ENGLAND.
For Tax/NI, if you are employing a nanny on a full-time basis, it is quite easy to do the Tax and NI yourself. If you are going to be sharing your nanny, then you may find it easier to use a Nanny Payroll company (such as NannyPaye, NannyTax, NannyJobPayroll) as it can get a bit messy when working out Tax/NI payments for a nanny whose time is split between two families.
If you are having a nanny on a full-time basis, then I've created an example for the first pay run. NannyNick's Payroll Example HMRC are very good now at providing new employers with help and advice, so don't be put off by it looking complex... especially if you have a PC, as HMRC provide a CR-ROM which will do a lot of the work for you, and you can complete a lot of information on-line now as well. Contact HMRC for a New Employers Pack .