I have been asked to clarify what the difference between ageplay and Daddy/Mommy Dom/mes & Littles, so here goes. This is from my experiences knowing ageplayers and being a little myself.
A person who role-plays a child of a certain age, and has sex as that child is considered to engage in ageplay. Most times, but //not always//, ageplay is full out sex, sometimes it only goes so far as being more than what is considered acceptably intimate, without the sex itself. If you ask an age-player his/her age, you will usually receive a concrete answer of the age they are role-playing. Ageplayers also tend to be much more flexible in moving in and out of their childlike role.
Littles are adults who being childlike is an innate part of their personality, even in their 'adult' mindset. Being a little is about expressing the inner emotions that you can't express in your "adult" life such as vulnerability, innocence, and dependence. A little's way to do this is to act childlike. A little usually doesn't have a specific age, but instead it will vary along a spectrum. Factors like their environment, the people they're with and their mood may affect how "little" a little is at any given point. Usually, a little doesn't snap in and out of their little mode right away, it's a progression into it and a progression out of it.
**Also please note that an ageplayer can be a little and vice-versa, but they are not mutually exclusive.**
Daddy/Mommy Dom/mes are usually in full control of their little, but also have to take care of the social and emotional well being of their baby girl or boy since their sub is in a slightly different mind space than traditional subs. Daddy/Mommy Dom/mes will have a series of rewards, rules, disciplines, and consequences with the mindset of their little considered. A traditional Dominant will rely on typical BDSM punishments such as bondage, paddles, humiliation etc., but these punishments will not work with a little and often will only aggravate the situation.
Another significant indication of a Daddy/Mommy Dom/me is that they will spoil their little. While this should be the expectation of all relationships, this is usually taken overboard by Daddy/Mommy Dom/mes. Daddy’s and Mommy's will know exactly what their littles love, and will reward them with gifts, outings, extra playtime or extra time in their little space.