We did school over the summer in preparation for our new baby girl who arrived on July 30. So, we are taking a few weeks off now instead of the summer. Anyway, we chose Who is God by Apologia for our Bible curriculum. I have an 8 year old 3rd grader and a 5 year old Kindergartener. We got the coloring book and the junior notebooking journal to use. The girls are so bored with this curriculum. I feel like it’s geared toward kids who are a little older. It’s pretty time consuming and they seem to get bored with all the reading. I think before we start up again, I’m going to try to switch to something different. What do you all suggest for younger kids? I want something they can understand, and I would like it to not take an incredibly long time because I don’t want them to lose interest in what I consider our most important subject. 
Christian Light Education is my favorite. I believe they are a Mennonite based company. My kids and I really enjoy this curriculum, and its a great price. Last year with my littlest kids we also read the story book bible "The New Bible In Pictures for Little Eyes’ and ‘101 Favorite Stories From the Bible.’ Both of these story Bibles have a handful of discussion/comprehension questions at the end of each story and each has lovely pictures. I haven’t tried anything else yet, but we have enjoyed the above options!
We use Bible Road Trip and it has options for multiple ages. It may still be free downloadable by week online although a few resource books are suggested. We love it! We take our time going through it and spend about 15 minutes to max 30 if we have time each morning. My kids (3rd and 1st this year) are learning a ton! There are suggestions for upper and younger levels with it too.
We also tried Who is God but it went over my 8 yo’s head. We will again try it in a couple of years.
We are currently reading from Leading Little Ones to God. It is excellent for a short everyday lesson, very mature and yet very easily understood. My 4 yo and 3 yo also participate in our discussions when reading from this book. They love the hymn selection as well.
We will, in addition to this book, be starting Bible Road Trip for my 4th grader. It seems like it’s going to be excellent for learning and reading through the entire Bible.
I have some other resources that my 8yo loves to read on her own, one of them is the Bible curriculum from ABeka. I purchased the lessons only and not the picture cards for $2.95 each I believe. I no longer read these but she does everyday to herself. She also loves the Egermeier Bible Story book. It’s amazing how much she knows from reading on her own.
Not to throw in too much confusion, but because I too find this is the most important part of education, I should also mention some other resources that I plan on using in the future. These are Firm Foundations: Creation to Christ, for children. There are two versions of this study for children. And then the Discovering series by Deeper Roots. These seem like really solid materials to add to your studies even if partly covered with the study through the Bible as your primary alongside.
I can send the links if you’d like to.
I hope you find what you’re searching for.
Take a look at Grapevine Studies. Your children won’t be bored with this curriculum! I would recommend getting the Level 2 for your eight year old and the Level 1 (maybe even the traceable) for your 5 old. Do a sample lesson and see how they do. Here is a link to the sample lessons at Grapevine http://grapevinestudies.com/sample-lessons/ 
This year we will be doing the draw to learn proverbs by the Notgrass company. It’s very inexpensive I think I payed $10 for the download and printed it for both of my kids. I have a third grader and a first grader. We are also going to read leading little ones to God which I love! And would highly recommend:)