The working hours in your host family are limited to 18 hours per week. Of course, this may vary over the duration of your stay. There may be more busy weeks and weeks, where you will have more leisure time. Therefore you should be flexible.
Your internship will take place full time, which means at least 35 hours per week.
As you can imagine, internship plus aupair will be an intense time. Be ready for this! If you are, it will be worth it! You will gain unique insights into Chinese culture!