Researching detailed information on autism and its spectrum disorders in a library or online is a time-consuming and sometimes frustrating process. To ease any anxiety you may have, take notes on only the most important facts regarding the subject(s). For instance, you can use a system of mnemonics in the form of an outline, diagram, "web," or graph to help you remember even the most complex information.
Come to terms with the difference between autism (e.g. "low-functioning" autism) and autism spectrum disorders (e.g. "high-functioning" autism). If your academic research does not help, set up an appointment or journalistic interview with a qualified mental health, child care or special education professional.
Don't hesitate to ask your friends, colleagues, relatives, etc. about any experiences they've had with people different from themselves. You may as well learn something about your own understanding of autism or autism-like behaviors in the process.
Because you are writing a story for children, don't use those "million-dollar" vocabulary words found in medical dictionaries, encyclopedias, handbooks, journals, etc. Rather, write in a style children can understand and enjoy.
Set a short length for your book. Obviously, the youngest of children don't want to read a book consisting of lots of pages. So, be clear-cut and to the point.
Clinically speaking, autism primarily involves social and communication impairments. Since these impairments are complex in nature, write in a simple style that appeals to children but preserves a realistic, rather than fantastic, sensibility. For example, jot down "He was in his own world" rather than "He was in his own world because ..."