It sounds like the situation is more complicated than the question. Usually in a family, a grandmother can talk to the parents about a problem with their child as it is assumed that all love his/her and have her best interest at heart. So, on the surface, I think it is okay to talk about something your grandchild has some issues with. As you ask that question, it makes me think that there is some tension there. So, is there more to the story?
Also, how old is your grandchild and what specifically is the problem?
patp, a 5 year old who can't make friends deserves some help. You probably have a very clear vision on what the problem is, as a grandparent. I'd say step in and offer your insights.