1. My kid is going to teach your child a bad word. Maybe not of the four-letter variety, but she's sort of an expert at stringing together verbs and body parts until she hits a combination that gets a charge out of her four older siblings (and will probably make the teacher suspect we've let her watch porn).
2. Frankly, she might also impart some of the four-letter variety. Forgive her; her mother's got a mouth like a truck driver.
3. Your kid will report that everyone else* has cookies and juice boxes (or whatever it is you don't pack) for lunch every.single.day. (*Except for that one kid with the filthy mouth. She's the fifth kid. Her mother's too tired for that sh*t.)
4. Some other kids will be able to read already. The teachers know what they're doing. Your kid will get there; relax.
5. Maybe your kid is the one who can read already. Oh yeah? Great. Can s/he ride a two-wheeler? I didn't think so.
6. Starting in the very first week, your child is going to meet and want to bring home a wide variety of exciting new germs and viruses. Resistance is futile.
7. Accept now that you're going to forget something. Sneakers on gym day, crazy hair day, lunch money, book money, library books, permission slips. Try to limit these moments to once a month or less, unless what you are forgetting is to pick up said child from school. That can really only happen once a school year or so, lest you give the kid a complex.
8. Befriend other parents on Facebook or your preferred social media crack of choice as soon as possible. You're going to be expected to remember the names of a lot of parents and kids all of a sudden. This is much easier if you start getting to see their names online frequently. Plus you can do a little stalking to see if that one kid has older siblings to explain the foul mouth, or if it's just sh*tty parenting.
9. Take it easy with the play dates, sports and clubs those first few months. Even if your child has been going to full-day daycare for five years, or five-day-a-week preschool for two, a full day of kindergarten just might wipe them out for the first month or so. Your child will probably not start napping again; instead s/he will opt for transforming into a whining, sobbing, disagreeable monster between the hours of whatever time you get them from school o'clock and bedtime. It, too, shall pass.
10. Lastly, hope that your child's teacher subscribes to the same theory my first child's kindergarten teacher did: She promised us parents that she'd only believe half of what the kids told her happened at home -- if we promised to do the same about what they said happened at school.