What happens when I visit a publisher?

The appointment normally lasts 15 - 30 minutes, depending on how busy and how interested they are. They will look through your work and ask you a bit about yourself.
Be enthusiastic and friendly.
Only say positive things about your work.
Make sure you have some colour copies of your best pieces to leave behind, with your contact details on them.

How do I make contact?

Make good quality colour copies of two or three of your best pieces. Post these with a short covering letter to the publishers you have researched. Try to get a specific name to address them to - the Art Director or Commissioning Editor are the ones you're after. If in doubt, don't be afraid to phone the company and ask who that is. In your letter, tell them that you would like to visit and show them the rest of your portfolio.

Follow up the letter with a phone call about ten days later, but don't be too disappointed if they don't remember your samples - they will get hundreds. Ask again if you can make an appointment to visit them with the rest of your work.

Where can I get more help and advice?
The best way is to join an organisation, like the Association of Illustrators or the Society of Authors (who have a children's illustration wing, CWIG). They will be able to offer you advice about your portfolio, who to visit, what to charge, what to do if you get a contract, how to publicise yourself and much more. They also send out newsletters and arrange talks and social events, where you can find out that there are lots of other people out there just like you!
Other useful sites to try
Further information
Visit Wordpool for free advice on presenting your manuscript, finding the right publisher, getting an agent, self publication and much more.
Books that might help:
For people wanting to become children's illustrators
Or do you want information on writing for children?
Books that might help:
Learn from my experience by reading my blog

Frequently Asked Questions

Put together a portfolio of self promotional work - between 10 and 20 pieces
Only put in work you are really proud of - quality is more important than quantity.
Don't try to be all things to all people - decide what style of work you are best at.
Illustrate actual stories - choose an existing book or a traditional story and reillustrate a couple of pages in your own style. This will demonstrate how you interpret text, as well as your drawing ability.
Put your best illustration at the very beginning of the portfolio, and your second best at the very end - that way you start with a bang but also finish on a high note!

How do start?
Do I need an agent?

Spend a lot of time in the children's section of bookshops. Familiarise yourself with what the different publishers do. Make notes - who publishes picture books, what kind of artwork do they seem to like? Who publishers chapter books? What styles of illustration are used for what age groups?

Get a copy of The Writers & Artists Yearbook (or something similar - there are a few different ones these days). This has listings of all the publishers with their details.

How do I know who to approach?

Probably not at this stage - unless you live in the Outer Hebrides, or are so painfully shy that you can't face the idea of visiting a publisher!
You will learn a lot more in the early stages if you do it yourself - publishers can give you vital feedback on your work.
An agent does make it easier for you if you aren't living in London, since that is where most of the publishers are based. But of course, an agent will take a percentage of your money for their service - anything from 10% to 33%. My advice is: try it by yourself first.