We have been using the Liping Ma, dd Gr. 2 and ds Gr.1, and it has been quite a challenge for us. We had a brief stint in China and I wanted to maintain their Chinese when we came back to the States. They go to a Saturday school which uses the Stanford curriculum and the families who attend are mostly all Chinese. I work with them during the week to do their homework (it is forcing me to improve my Chinese) and they also have a tutor once a week. Because of the lack of pinyin it has been a bit of a struggle for me especially for the Gr. 2, not so much for the Gr. 1. The CD-Rom that comes with the curriculum is invaluable to us. It is a very strong and solid program which is good for us and it has forced me to keep up with my Chinese. If you do not have access to a local Chinese school then, depending on your commitment, you could do the Gr. 1 program with your oldest and have a weekly Chinese tutor. My biggest advice is to make sure it is a daily practice.
HTH :)
Pancha