It takes more than the desire to help children to become a teacher; it requires getting the necessary education certification in order to practice in the state of your choice. Nine times out of ten, you have to become a student yourself before you can take on the responsibility of teaching them.
Each state has its own licensing requirements, so your first decisions have to be where and what you want to teach. Education certifications vary from the very specific to the incredibly broad. You can be certified to teach anywhere within an elementary school system, or you can focus your training to more explicit needs, such as adult literacy, special education, or administration.
Some states also provide what they refer to as an alternative teaching license. This is to provide an education certification to individuals who might not have followed the traditional learning route, but have gained a vast amount of knowledge in a specific field. These can very greatly from state to state, however, so if this is the path that interests you, it's vital to confirm program requirements before making any kind of decision.
While it's not a necessity to get an education certification in order to teach, it's in your best interest to do so. All public schools require their teachers to be licensing; by opting not to get certified, you are dramatically limiting your choices to private institutions in looking for work. In addition, education certification proves to employers your commitment to the field. You teach best when you're willing to continue learning.