Well, I can tell there are other people here vastly more qualified than I to give you advice on what you should do.
But I can tell you what you shouldn’t do, at least as long as you’re looking to make money from writing.
I wrote and illustrated my own graphic novel. Not the same as an actual written novel, I know, but I did go through the rigmarole of self-publishing. There’s plenty of options, but if you go that route, funding is a big issue. The service I used to produce my book (which anyone can still buy since it’s print-on-demand, which is nice) charged me about 40 USD per copy. I was able to buy about 15 of them for myself at a small discount, but I wasn’t keen on charging people $45+ for a book, so I literally don’t make any profit from them.
Now, there’s some caveats to that since a graphic novel has a lot more expensive requirements than a written one, but that’s how that worked for me. Amazon does print-on-demand self-publishing as well, but they have different requirements and from what I’ve heard it can also get pretty expensive.
So not to say it can’t be done, because I know plenty of people have self-published their books and made some money from it, but the initial investment and push to sell your book all has to come from you. And on the worst-case scenario side of things, you buy hundreds of copies of your book to sell that no one buys and you have dead stock.
So if you’re dead serious about writing and want to make money off of it, and keep doing it, then I concur with everyone else in trying to find a publisher.
On a more general side of things, though, I’d personally be more concerned with the actual writing part first than publishers and money making. A children’s book under your belt is pretty awesome, but a novel is a whole other beast.
If at this point you’re just “considering” it, you need to change that status to “I am doing it, currently.” Getting serious about it is the only way it actually gets done and pans out.
As for having higher chances of actually finding a publisher, it also helps to have plenty other experience. You’re jumping the shark from children’s book to novel. If you can, it always helps to try and get published in smaller formats: short stories, articles, essays, the like. Not only does it help you improve in the craft, it also builds your credibility and portfolio. If publishers see you’re a prolific writer and that you’ve published a number of stuff before, they’re more likely to take you on.
@T4k4nuv4 also made great points about digital publishing. A very large portion of the book market makes sales through Kindle and other eReaders. I know quite a few people asked me if my graphic novel had a digital version. It’s easy and convenient for people, and you don’t have to worry as much about distribution and covers and print sizes and all that jazz.
As a final point, I want to offer some alternative measures of success.
My graphic novel didn’t sell. Sure, like a handful of people bought it that weren’t friends and family, but it was at-cost and I saw none of that money. I actually lost money buying copies to give to other people who helped me make it.
Despite that, I count it as one of my greatest successes. It was something I had always dreamed of doing, but never really felt I could ever do. It kicked my butt while making it, I learned a ton while doing it about writing, art, storytelling, printing, publishing.
It also completely destroyed my sleep schedule from then on and I haven’t gone to bed at a good time since.
I made no money, I have no publishing deals, and no sequels are in the works. None of the things you’d conventionally ascribe to success. But for me, as cliché as it sounds, the creative journey was worth every second of it. And maybe one day it will lead me to something I can pay the bills with.
So ask yourself what you really want out of this project. I’ve seen plenty of aspiring authors pedaling their books at fairs as hard as they can and not seeing interest coming their way. I feel for them every single time, but every time I do hope that what they made was worth it for them.
I do wish you luck in this, and I wish for every measure of success to come its way!