I don't think you need to worry about "seeming like a kid's book," I think you need to worry about making a professional submission. On two points:
- Why do you think your novel should have illustrations, when most don't? Do they add anything more to your story than similar illustrations would to other books in your genre? If not, then whatever considerations apply to illustrations in most books, probably apply to yours as well.
- While "good drawing skills" are great to have, even if a publisher is persuaded he does want to include illustrations, that by no means implies that he wants yours specifically. Illustrations will be a huge element of book design and presentation, and it's generally very important to the publisher that he keep complete control over that.
If you're self-publishing, then neither of the above apply, and I see no reason why illustrations shouldn't be a colorful addition to your work. But the same considerations the publisher might have should still be considered: you want to make sure your illustrations are really appealing and look professional enough to include in your book, and that they're inserted well into the overall design and layout. If not-so-great artwork is inserted in a careless manner, that might make the whole book seem very shoddy.