I have two children that were in private Christian school for 5 years. My son only used Abeka during those years, so when I decided to homeschool two years ago, I chose mainly Abeka because I was green and because I knew I could trust Abeka to cover the bases. (and because my kids were very familiar with the curriculum) I have never purchased the parent kits. I always buy the teacher's books used on eBay or other internet sources. You can save a ton of money that way. The first year I tried to save additional money by not purchasing new consumables, but that was a big mistake. It caused much more labor for me and them. If you attend one of the show cases, (materials displays) you can pick up a catalog, that way you can look at the list of materials that are available for your child's age.
One more piece of advice about the age level of the curriculum to purchase. Abeka is an advanced curriculum, was your 6 yr. old in Kindergarten this year? Abeka is a high phonics based program and they begin reading in K5 (kindergarten), so, I wouldn't jump to 2nd grade. I would stick with 1st grade for your 6year old (for the fall) and kindergarten for your 5 year old. That's just my opinion.