I have a colleague who told me about her experience. She invited her mother-in-law to come over to look after her daughter. Everytime she used the excuese of taking care of the granddaughter and got rejected almost 10 times. Then my colleague asked the Senator to write a letter and she got a very formal letter from the Embassy. Among the several reasons they provide is the concern about her intention of staying over time for taking care of the baby.
Then when the girl is in elementary school, the grandma finally got the visa. This time she was also asked why she wanted to come, was it for grandkids? She said, no, they go to school now.
This is a bad excuse to use.