E.L.
i just spent 6 yrs down there, and we never went to Fiesta, i would have like to gone but not with my kids, and since we had no family there we never left the girls. I would go when Fiesta was over personally, San Antonio is awesome place they have so much to do, Sea World, Six Flags, downtown they have a children's museum and the River walk is beautiful, there is a fun restaurant down at the river walk Rain Forest Cafe it is fun for kids. Also Schlitterbahn (SP?) water park is a short drive in New Braunfels, also in New Braunfels they have an awesome drive thru safari thing, i could go on forever about San Antonio, i really miss it there...
good luck with you decision, but i agree with the previous lady who said it can get dangerous to have kids out there at Fiesta. And very overwhelming.