How do I teach kids at very different developmental levels?

You can teach young children now, but the developmental range still challenges you, the fact that in one room children are at wildly different stages all at once. That is genuinely one of the hardest parts of early teaching. Being challenged by it is a sign you see the children clearly, not that you are failing. The range is not a problem to solve so much as a reality to meet. You cannot teach a room of young children as if they are one child. The skill is offering the same activity in ways that stretch each one where they are, and that skill grows with watching and adjusting, child by child. Pick one activity this week and think through how it could work for your most advanced child and your least advanced one at the same time. Plan those two ends and the middle takes care of itself. Do that often enough and meeting the range becomes second nature.