I actually had someone tell me this the other day.
My 7 year old twins are not my DH's (biologically....but in every other way, they are his) and DH and I have a DD together. We were at the park and someone commented on how different my twins look than my DD. I said that DD favor's my husband more than me and the twins favor me more. The lady then pipped up and said that DS doesn't look like me that much, to which my sister told her that they have different birth father's than my youngest DD. The lady looked at me all disgusted and said "Well, that's just trashy.
My twins will be 8 in July, DD will be 3 in August. There is exactly 5 years, 1 month and 1 day between the twins (who are boy/girl) and YDD. I don't think they look that different, do you?