I feel bad about this, but I have no clue if it's a normal way to feel and I can normally guess what Mumsnet would say so don't bother, but I really don't know about this.
I was in the park earlier with DC (5 and 9) I always sit on the bench closest to the only exist.
There have been a couple of times when a father (who clearly has DC at the park) help youngest DD onto the monkey bars for example, then just go with their kids on to a different bit of equipment. We are a friendly village and do tend to interact with the DC (if it's obvious they go to same school, etc.)
However, I've had it once where (and this is with 9 year old DD and no contact involved) a man was pointing to bits of the rope that DD should put her foot onto (you know, to help her get to the top) and I went over and made casual convo and he had no children there 
Is it wrong to have not even thought for a second about that dad, but felt uneasy about that man for the rest of the time while we were there?