good advice healthy11. same happened to me when i relocated back to us from south america. there is much to share.... but healthy11 covered the bases.

Welcome! Every school district is slightly different in terms of how they handle enrollment. Some are very specific and where you live determines which school your child attends, while others have "school choice" or "magnet school options" and there may be a "lottery" for open seats in other schools in the area.
Your best bet it to phone the school district you're interested in, during their normal open hours, and ask what they require. A local real estate agent might be able to give you some advice as well, but I wouldn't buy a home without verifying with the school district, that it's in the school zone you want your children to attend (sometimes school districts change their boundaries from year to year to prevent overcrowding....)
It will probably be best to get certified copies of your children's birth certificates and regular copies of their school and medical records before you leave your current country. Once here, they may need additional vaccines to show their medical charts are up-to-date... I hope this helps.