Honestly I experienced the same thing when I hired 鐘點 (half day for one month). Need to go home at 7pm and then 要求多多, expensive ($50x6 hr=$300 per day) but not worth the money.
I know a few families (Hongkongers) living in Beijing with local nannies. Those nannies speak excellent Putonghua and educated with high hygiene standard. I always see Phili/Indo helpers share same drinks with the kids in the street (一人一啖). Depends how you train your helpers.