Review the state math curriculum standards for the Kindergarten, first or second grade class that you are teaching. Open-ended questions are appropriate for these grades, but you still need to make sure that you adhere to the standards.
Create your lesson plan as you normally would and deliver it. Using open-ended questions does not change what and how you teach.
Create a set of closed-ended questions for the lesson. By doing this, you are giving yourself reference material from which to develop the open-ended versions. For example, you may be teaching students to add money. A closed-ended question for this skill would be: "You have three quarters, two dimes and a nickel. How much money do you have?"
Review the closed-ended questions that you developed. Use these to develop the open-ended versions. For example, if you previously asked for all of the prime numbers between 0 and 20 (a closed-ended question), now ask the students to list three prime numbers in the same range and then explain what makes them prime. With open-ended questions, you are asking students to explain their thought processes instead of simply providing a correct response.