It is very normal for children to experience fears. It is a part of life for everyone. Do you remember being afraid of the dark, or storms when you were a kid? I was afraid of both, but now I love storms. Funny how that happens…one minute it is a major fear and the next, you have faced and embraced it without even realizing it happened.
Both of my older kids have had issues with fear around the age of two. After a lot of research about the subject, I found that this is an age where they are developing fears and many of them are afraid of the dark, sleeping alone, etc. We solved a lot of this by letting them share a room. It is a temporary solution, but for now, it has worked perfectly! They have each other and they have both slept much better than before. If your kids are experiencing fear, just know it is normal and try to make them feel as safe and comfortable as possible (without giving in too much).