We have decided to start homeschool next year. I've seen a lot of questions about placement on the board, but I feel like I need reassurance for my particular situation (I hope you don't mind)

We have a son who will be 9 in Sept (currently in 2nd grade, public school) and a daughter who will be 7 in Nov (currently in full day Kindergarten, public school). They are both reading 1 grade level ahead and are strong writers. They are good listeners, love to be read to, and have great attention spans. For math, they are at grade level.
After looking at the Placement Charts, I think my daughter might be able to do Bigger; however, I don't believe she has had much exposure to parts of speech or anything more than basic math (i.e. 2+2). She does tend to act and think older than she is. As for my son, I think he could almost fit into Preparing, although he hasn't had cursive yet and I'm not sure how strong he is at knowing the basic parts of speech. And... he is average at math.
Because this is will be our first year homeschooling, I was hoping to do a combined program for them just to make things easier. I was thinking about having them both do Bigger, but I don't want my son to become bored or held back in any way. I also don't want to push my daughter into something that she might not be ready for.
Thanks in advance for any advice you can give.

Jen