Just went to a Q&A with some Cirque du Soleil - La Nouba performers Saturday afternoon. This is definitely an amazing show for kids aged 7 and 9, they will be completely enthralled.
As for where to sit, for a first show, I would go for 2nd tier seats in section 204 if possible - those will give you a great general perspective of the show. There is so much going on that it will help you to see the overall tableau which IMO is the best initial experience of the show. Then, when you come back, get seats in section 103 toward the front in order to feel more connected to individual performers.