Are you doing Cash Based Accounting - so putting things through your accounts when you get paid, when you spend money? That has been available since 2013/14 tax year and is probably the easiest way to do things.
I am a nanny, employed by two families but also do ad-hoc work which I do SE. I started this in October and am getting my tax return done over the next month.
So you are doing your Self Assessment return for your accounts October to 5th April 2014 I guess. Then starting a new tax year 6th April 2014-5th April 2015.
There will not be much in terms of things you can claim but you should be able to put down as expenses in your accounts:
Advertising
Stationary (such as buying the accounts book, a bit of paper for producing invoices, small notebook for use as mileage log).
Accounting software or cost of an accountant
Mileage driven with children. You may be able to claim mileage from your home to the child's home and back but I am not sure about that.
Toys and equipment used only for the business.
Parking costs such as on outings (if you are paying it, not the parents)
Admission costs for outings (but wouldn't the parents be paying that?)
I would avoid claiming for anything that could be considered is for personal use or use in an employed job. It needs to be business expenses, so things that are only needed for the business.
"Oh yeah it's great, you can claim tax back for haircuts and clothes and things." hmm
No, I would not attempt to claim that sort of thing.
If you want to go around with a large logo on your t-shirt, then maybe that t-shirt and logo printing are claimable... but non-logoed stuff is unlikely to be claimable in my view.
Also, do you need to keep receipts or logs of everything?
Yes ideally. Certainly keep logs for all mileage done.
The biggest things are clothes and diesel.
Clothes - unlikely to be claimable in my view. Most likely to be considered as a personal item.
Diesel - claim for mileage not for fuel cost. Note down start and end mileage of every business trip, such as taking children out somewhere.
HMRC: Self Employed Expenses
Simplified Expenses for sole traders
And could I claim mileage costs to and from my self employed jobs?
I don't know. Travel with children is claimable but not really sure about the to/from place of work. Personally I wouldn't but factor it in when deciding how much to charge a client for childcare.