As long as you have UVA/UVB lighting (or the ability to place their cage outside most of the year), sufficient heat, ample room, and a VARIED diet the little one should be good to go. You can keep them in a tank when they're babies if you must, but they grow fast. I never was one to support free roaming iguanas unless the house is completely iguana-proofed and kept quite warm, but if it works...

I built my old iguana a 4x3x2 cage of wood and wire (stunted growth from MBD, she was only 2' or so) with branches and greenery and a 'pool' on the back half that stayed outside most of the year. This was in Texas, tho, I'd never be able to do something like that now.