"they were going to have Kαtααng, which they insist is in the “DNA” of the show, happen with a ten and twelve year old?" That's because Kataang was supposed to remain one-sided with Aang crushing on Katara but her not reciprocating. Them actually getting together was not planned out until later on. Even during Book 3, some of the writers wanted Katara to end up with Zuko. Zutara happening was not something that Bryke wanted but the other staff members and Aaron Ehasz wanted it to.