I work for a publisher.
My best advice again, is to check out
www.literarymarketplace.com
It is an excellent site to start out with. It lists all US and many non US publishers and it will tell you , usually if they will accept unsolicited manuscripts.
Most of the "big" ones do not accept manuscripts unless they come direct from a literary agent. If you really think that you want to get into writing book, an agent is the best route to go. A good agent will usually not expect a lot of money up front because they think you have potential.
There are also web sites where you can self publish and companies where you can self publish. And of course, some of the smaller publishers accept unsolicited manuscripts. Keep in mind that these publishers have smaller front lists each season so they print fewer books. Therefore you might not have as much luck with the smaller ones simply because they get more volume of manuscripts.
If you do get an agent, DO NOT, I repeat DO NOT get discouraged if you are turned down the first 800 times you submit something. Big publishers generally print about 30- 40 new books a season between all genres (i.e. 6 new kids books, 7 new adult hard covers etc.) and these will include new ones from their established authors who are under contract. What you are writing just not fit into their print schedule or they may already have something similar to what you are writing set to print (i.e. If you write kids ABC books and they already have a new one for this year).
If you do kids picture books, as a rule it is easier to get published if you let the publisher select the artist from their list of contacts. Unless you do the writing and art both yourself.
Again, that website is a REALLY good place to start.