I'm pretty sure that there are guidelines by the goverment about that, not sure if it's state, county, country, etc... You can ask the local schools about the curriculum and how to homeschool if one decides to. There are plenty of sites online about this subject as well, just google it.
For preschool I'd suggest that you work towards letter recognition, sounds, and possibly by the end starting to read. Writing skills, how to hold a pencil correctly, write their name, etc., They should be learning number recognition, how to count to 20, their full name, shapes, colors, and about animals and family interaction.
Arts and crafts are ALWAYS fun and you can make them a learning activity too.
at 9:12 PM on May. 18, 2009