Make sure both villagers are adults
Make sure both villagers are willing
Give each villager enough food, such as 3 bread, 12 carrots, 12 potatoes, or 12 beetroots
Place beds with at least one extra bed for the baby
Make sure each bed has at least 2 blocks of air above it
Keep the beds accessible to the villagers
Keep the villagers close enough to the beds
Make sure the village is valid and the villagers can pathfind to the beds
Remove threats like zombies or other hostile mobs
Keep the area well lit and safe
Wait for the villagers to enter breeding mode and produce a baby villager