As you have noticed, restricting the number of children to 2 (like the binary trees earlier) yields a tree that only lets the algorithm decide whether to go left or right, and it's easily hardcoded. Additionally, storing only a single key-value pair in a node can be seen as a waste of space—after all, the pointers can be a lot larger than the actual payload!
B-Trees generally store multiple keys and values per node, which can make them more space-efficient (the payload-to-pointer ratio is higher). As a tree, each of these (key-value) pairs has children, which hold the values between the nodes they are located at. Therefore, a B-Tree stores triples of key, value, and child, with an additional child pointer to cover any "other" values. The following diagram shows a simple B-Tree. Note the additional pointer to a node holding smaller keys:
As depicted...
