DD is 6 months and is very happy and amenable 90 percent of the time. Only really cries when she's tired (hope I am not jinxing things by writing this down!)
She is happy and smiley with everyone (including strangers) except my FIL. She cries when he holds her and really doesn't even seem to like him being close to her unless I am holding her.
This has been going on a few months - the first time we noticed was when he came round one evening and we passed her to him (perhaps a bit quickly). We put it down to the fact that she was tired and hungry but now it seems to happen every time she sees him.
I'm sure she'll come round eventually but it's obviously not very nice to for him in the meantime!
My DS was scared of my dad for quite a while and I felt awful. There didn't seem to be a particular reason. After a while he was like it with a few other males but we didn't push him to sit on laps or anything and just got the person he was wary of to carry on doing there thing or offer him toys and he soon came around and now he gets excited when he sees his grandad. He was a bit older than yours but they do come around in their own time, just don't push them. Hope this helps.