ermm... yr child not having any medical conditions, right? At 20mths she still hasn't walk and lifted her head at 6 months, started to sit around a year and crawl around a month later is kind of slow. Have you gone for yr routine Child Dev Review as per the Health Book? What did the Dr say? Did he refer yr child for any further review/check-up?
I know it is frustrating when strangers ask, ''how old is she?'' ''Why cannot talk or walk yet .... I'm having the same problem. But I have medical reasons to ask them to 'shut-up'.