I agree that you should rather go eclectic. My 6 year old and my 4 year old both have skills on different grade levels and so we work on whatever level they are at for each subject. We do loads of lifeskills at this younger age and although we do stuff around each subject, right now we mostly pick one or two things and have that as our main focus for a while until we all want to move on. It could be swimming, or learning to ride a bike or learning to type or use powerpoint. Recently it was the Chinese New Year, baking and working with money and now for Aiden Cursive / joined up writing. It's more fun like that at the younger years and they actually get through a lot of work without anyone realising.
We have workbooks and other fun games for teaching some curriculae type things, but we mostly do it as described above. It's working better than anything else right now for us.
The other thing to remember is that no decision has to be forever. You can always switch, change the mix etc. I love that about home schooling.
also remember about buying a ready-made grade-level curriculum that you are more likely to need at least 2 per year if you are only sticking to their stuff and guidelines. Your child will more than likely fly right through that and then it becomes a rather expensive thing too.
