Chairs are hard.... when you don't use plans.
I used Ana's plans for round 2 of these chairs. I actually feared for my children's safety with the first set I made using no plans at all. With plans in hand, these turned out excellent and were actually quite easy to build.
I used 1x2s for the legs, 1x3s for the side supports and for the turquoise back panel, a 1x4 for the pink back panel, and scrap MDF board for the seat base.
I regret using the MDF board, it chips easily. In hindsight, I should have used 1x3s for the seat bottom.