Cytokinin
Cytokinin is a plant hormone that tells stems and leaves to grow new buds and branches.
Think of it this way
A cake recipe tells a baker to add extra layers at each step. Cytokinin works the same way in a plant. It signals the stem to sprout new buds and branches at each node. More cytokinin means more growth points along the stem.
Explaining cytokinin by grade level
Plants make something called cytokinin. It helps new buds grow on stems. When a plant has more cytokinin, it grows more branches. Add it to a plant and watch new shoots pop up.