The kids play in the crypts. Bran is as little as Rickon is at the start of ASOIAF, three or four.
<Robb took them all the way down to the end, past Grandfather and Brandon and Lyanna, to show them their own tombs.>
Here no mentioning of Grandmother or a tomb either. But she probably wasn't a Stark so if she was dead her bones were probably given back to her House.
I suppose if Catelyn had died at Winterfell she would have been brought back to Riverrun to get a Tully river-funeral.
I have high hopes for the companion book for ASOIAF and that there is more information given about the Stark lineage.
But the crypts were for the Stark lords only. The only reason Lyanna was there, iirc, was because Ned loved her so much he buried her there.
For that matter, what happens to other Starks who aren't lords of Winterfell? Is it ever mentioned where they are buried?
As for Ned's mother - as much as I'd like to know more, I think there's waaaay too many characters in the books already to follow what's happened to everyone. But it'd be nice to hear at least something like "she died when Ned was little" or whatever. But then there'd surely be 100s of conspiracy theories coming up about her death, so maybe it's better she's never mentioned at all