It is truly fine to begin homeschooling your child at any
time during the year. (school year or even in the middle of the summer if you want) My two oldest sons were both attending private school (4K and 2nd grade) and I pulled them out 6 weeks into the year to homeschool them. I think it would be great to begin homeschooling them in Jan. but it is your personal decision. (One of my reasons would be to save the tuition money that you would spend for the spring semester and spend it on homeschooling curriculum instead.) Homeschooling is way
cheaper than private school tuition. Also, I think your children are going to enjoy homeschooing so
much more than tradtional school...........so why not start right away?
If you buy some first grade curriculum, keep in mind that if you only use it for a half year now, it will then be passed on to 3! other children so you will definitely get your money's worth.
Before deciding what curriculum you want to purchase, I recommend reading reviews first. Here are some links for that.
I love to order curriculum from Rainbow Resource. They have low prices and a huge selection. They also have product reviews.
Congratulations on your decision to homeschool. I think you're going to love it! Best wishes.