Before you leave, make sure to lock the door.
1. - Of course, I will.
2. - Sure, I will.
3. - OK, I will.
4. - I know, Mom.
5. - I see, Mom.
(Are the answers all correct and natural?)
Yes, they're fine.
Also these:
OK!
Sure thing.
All right.
All of the answers provided are correct and natural responses to the statement "Before you leave, make sure to lock the door."
The choice of which response to use depends on personal preference and the level of formality in the conversation.