Okay kiddo, do you know the alphabet? We have ABCDEFGHIJKLMNOPQRSTUVWXYZ, right? Now, out of these, there are five special letters called vowels. They are A, E, I, O, and U.
When you say these five letters out loud, you'll notice that your mouth is open and your voice comes out smoothly. That is because these letters represent sounds that are made by letting air flow freely through your mouth without any blockage.
Other letters, like B, C, D, F, G, H, J, K, L, M, N, P, Q, R, S, T, V, W, X, and Y, on the other hand, need your mouth to make some kind of blockage, like closing your lips, pressing your tongue against your teeth or mouth roof, or tightening your throat, in order to make sounds.
So, that's what makes vowels special. They are letters that allow air to flow freely through your mouth without any blockage to make different sounds. In fact, every word you say has vowels in it and they help make the sounds that make words sound different from each other.