We have a fair amount of this also and I think it's pretty silly. It happens w/ two of our three sets of grandparents, and with one grandmother in particular it feels competitive and over the top.
My kids are not quite 3.
None of our grandparents are local so that mitigates the impact a bit, and I also think that time will prove that the kids are bright and lovely, but fully within normal ranges of most things.
In the meantime I just mostly ignore. When I'm pressed for a response re their thinking some particular thing is hugely advanced I say things like "Maybe, I don't know. But yesterday he couldn't find his was out of the room so I'm not holding my breath." Or "Well, they're having a language surge, that's for sure. It will be fun when they take a coordination leap also." Or "You know, I don't need or want them to be gifted. If they are that's great but it's far more important to us that they are happy and kind, and emotionally intelligent. That's what we're focussing on." Etc...
Maybe with your own parents you could be a little more direct, but that's how I dodge my MIL's pushiness when it bugs me.
Also, it's possible you're projecting some of your own stuff and putting a little too much weight on the importance of the things grandparents say. Especially if it's your parents in question - you're more likely to react more personally than to things said by less close connections.
Try to ride it out. Your child will be brilliant at something and rotten at something else. Your response to that will matter INFINITELY more than a grandparents.