Why do you put the games in Adult/Child timeline?

I want to know why do you put the games in Child or adult timeline

Because a split occurs in the timeline due to the time-travelling of Link in Ocarina of Time. Therefore, some games take place after the events in the adult portion of Ocarina of Time, and others take place after the events in the child portion of Ocarina of Time.

Your question is a tad confusing. Do you want to know why a given game is placed in a given timeline (ie. Why tWW is adult) or do you want to know why we use two timelines in the first place?

I want to know why a given game is placed in a given timeline.

Thought so;

Well, Wind Waker (Adult), Majora's Mask (Child), and Twilight Princess (Child) are obvious; confirmed by developer quotes and their OOT connections.

The Minish Cap, if placed after OOT, may be placed in the Adult Line because of its connections to tWW (eg. Possible Flooded world, mention of Triumph Forks, etc.). In itself, it has no connection to the child line. It may also be placed based on its FSA connections.

Four Swords Adventure (and, by association, Four Swords) may be placed in the adult timeline if one assumes that Dark Mirror = Twilight Mirror (It could not occur after TP where the Mirror is broken) but more likely It will be placed based on its relationship to AlttP, or possibly even TMC.

The Oracles may be placed in the child line if one becomes very picky concerning Twinrova (Because Twinrova died in the adult, some would rather OOX be in the child). More likely, they will be placed based on their relationship to the other 2D games.

A Link to the Past (and, by association, Link's Awakening, Zelda I, and Adventure of Link) is the kicker; there are about 500 posts near the top of the forum right now concerning its OOT relationship. If a solid placement for FSA is alredy determined, it can be used to easily place AlttP.

As mmmmm_PIE mentioned, WW, MM and TP are confirmed.
About others.
TMC, FS, FSA, ALttP, LA must be in same timeline, and must be in adult, since they feature dark realm (created by Ganondorf in adult ending). Also, since they are after split, LoZ and AoL must be in adult, since they were confirmed being after ALttP.

Oracles prolly come between ALttP and LoZ.

Edit: Phantom Hourglass ending will be really important, since it can end doubts about placement of TMC-FS-FSA-ALttP-LA-LoZ-AoL

Originally Posted by CassSept

As mmmmm_PIE mentioned, WW, MM and TP are confirmed.
About others.
TMC, FS, FSA, ALttP, LA must be in same timeline, and must be in adult, since they feature dark realm (created by Ganondorf in adult ending). Also, since they are after split, LoZ and AoL must be in adult, since they were confirmed being after ALttP.

Oracles prolly come between ALttP and LoZ.

Edit: Phantom Hourglass ending will be really important, since it can end doubts about placement of TMC-FS-FSA-ALttP-LA-LoZ-AoL

The Dark World could have been created by Ganon/dorf at any time, since we don't know exactly when the ALttP backstory happens.

After TWW, I put the FS games. Partly because I like to seperate the new from the old, and partly because PH might be a game linking TWW to TMC. I put the older games in the child timeline partly to seperate the old from the new, and partly because I like to put both Oracle games in the child timeline, and I need ALttP and AoL to explain the state of the triforce in the beginning of the Oracle games.

I tend to agree with Daphnes.