That should be our number one! After that, it will depend upon circumstances and your child. Years ago we were foster parents and I had four children in our home to school. Now I don't want to give you the wrong impression that we were homeschooling, officially, the oldest child was in school and the other three littles: One was in kindergarten and the other two were littles for sure! But it was after our foster son went to public school that I found out what a challenge it can be to teach with littles around~and the multi age range teaching. Our older foster son was third grade and needed my help to learn his math facts: addition, subtraction, multiplication, and division. My kindergartner was active and played hard having spent his day in public school as well...then there were the two preschoolers. What I did was worked with our older boy one on one and let the littles play quietly with "quiet" toys. Quiet toys are ones without bells/whistles/ noise boxes/lights and sounds.
Here are some ideas:
1. Puzzles (age appropriate~I used to collect these up so I had a lot and when I got them out it kept them very busy!)
2. Coloring sheets/books
5. Lincoln Logs
6. Matchbox or Hot Wheels cars
8. dress up clothes (costumes and larger "play" clothes for pretending)
9. writing paper and pencil
10. books (I would put books and say, "Let's read." and encourage looking at pictures.)
11. Audio volume controlled headphones with stories on cassette, Mp3, or dvd. I don't suggest movies as much, but maybe on occasion. The audio story will build listening skills.
Very young children will need loads of patience while schooling older siblings. If you have several older children, you could have one look after the youngers while you work with an older. Of course, do what will fit your family. One thing for sure, if a preschooler isn't kept busy with something they will be "into" the schooling of the older child or children. Busyness is just in their little natures and curiosity is in their hearts! Love 'em by keeping them busy with age appropriate activities while you work away with your older child.
We made it working with all the ages. Everyone was learning, even our littles who were learning the wonderful skills of imagination, ingenuity, coordination, and more!
Don't be afraid of working away while littles are around. Love 'em and keep them learning too!