My two at that age were both very suspicious of me, which I think is quite healthy. I kept my distance. They stay with me (with their parents) three times a year for a week at a time, and by the end of each visit they were friendly but not huggy. When they got to three, things changed. Not overly huggy, but they would sidle on to my lap if they wanted a story. They were cared for by their other grandma for three days a week for a while, and once she came up too. Only the older one wanted to know me! It was a bit upsetting, but I know that they get very excited when they know they are coming up here to stay, they love it.
They don't hug her either. They just sit on her lap. We both get kissed goodbye, as DD was very affectionate it does feel strange to me, but she says they have always been like it with everyone, very suspicious until they know people well. Just because I am a blood relative, it does not mean that they know me. The six year old is perfectly happy straight away to see me, the three year old takes an hour or so still to settle down and stop glaring at me! I think it's quite funny. I laugh at her and she then relaxes.