Angela has valid points and it may be true that you branch out later but this is a great way to get a feel for what you are doing. My daughter entered 3rd grade this past fall, it was her first year in a "real" school. My second son who just finished 5th was with k12 for 2nd-5th grade, he will go our local schools next fall.
It is very structured, but it doesn't have to be. Yes there are things you have to do but you can bend the system to work with you and not against you. If the objective of a lesson is that your child learns a specific group of sight words then it doesn't matter how you get there, only that you did. This goes for tests as well, or what they call assessments. Just because it is laid out a certain way does not mean you have to do it that way, my son was involved in a pilot program this year and worked with teachers daily for math and language arts/literature and science. They went over the material, they tested the kids in online classrooms and I just plugged in answers and marked the written assessments complete.
This is fine as long as your child knows the material, which means you can skip ahead as fast as you like or take your time and repeat lessons. It is annoying that you can't just skip over things in the computer though, you have to mark the answers for the tests, even if you skip the test, or it isn't counted as complete.
The materials are great, my daughter did very well transitioning back to public school. She's social and popular, academically ahead of her peers and got excellent grades.
There are also a ton of great resources once you get started, the yahoo groups are very helpful. Ask questions and don't be overwhelmed when the 101 boxes show up, they send you everything you need and then some it seems like and while exciting it does lead to those OMG what should I do with all this moments.
Your other child will likely be your biggest challenge, you will have to teach your older child to work on their own at least a little, because it will take up to 5 hours out of your day, time when you can't easily be entertaining the little one because the older needs your attention. Part of why I allowed my kids to go back to school was because my 18 month old and 4 month old made teaching difficult (and they wanted to go). Keep a school box for the toddler with things she can do while you do school work.
good luck. hopefully this post makes some sense I'm kinda all over the place trying to type with the baby :)