Prepare the tin before peeling the bananas. Once wet and dry ingredients meet, the batter should go to the oven without a long wait, so lining first keeps the pace calm.
Use a wide, stable bowl for mashing and put a damp cloth underneath if it slides. Begin with a fork to squash each banana against the base, then stir; tiny soft lumps give the child a realistic stopping point.
Melt the butter early and leave it to cool while the bananas are mashed. Warm is fine, but very hot butter can make the egg form cooked threads. Crack eggs into a separate cup so a shell rescue does not disturb the main bowl.
After flour goes in, switch from energetic mixing to slow folding. Scrape from the bottom and turn the batter over until the final white streak disappears, then stop. A few banana lumps are better than an overworked batter.
A central crack is normal. Keep the oven closed for the first 40 minutes, then let an adult test the deepest point. If wet batter clings to the skewer, bake for another 5 minutes and check again.
Give cooling a real place in the sequence. Ten minutes in the tin lets the loaf firm without steaming itself soggy; after that an adult can lift it to a rack. A warm slice may smell tempting, but full cooling produces much neater pieces.