The most traditional type of swim cap is usually found on competitive swimmers. They do come in fun designs to help you stand out. Waterproof, so your hair is away from the pool water, and smother to maximize resistance.
Fabric swim caps are an alternative to silicone swim caps. The main difference is that they aren't waterproof, so your head will still be wet. This can help with relieving heat on your head and still does reduce drag, just not as much as a silicone cap would.
Swim caps aredesigned for fun. Kids don't usually want to wear swim caps as it is, but these designs make it just a bit easier for them. Good luck getting a kid to wear a plain cap