Been there, done that.
On thing about being a Grand Parent, the kids go HOME, after a visit, and you can get on with whatever. 
I concur. First grand daughter was born last August; second grand daughter (different son) is due this August.
Seems like there are a lot of Grandparents here.
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And that is very cool too!
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In
MY case, We've only got one child (our Daughter) and she's "Special Needs" (as some of you know) and won't ever marry, much less have kids. But, that's fine. We've resigned to that a long time ago and we're okay with it.
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Sure, I'd like to have Grandchildren, but that's the way it goes.
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Nothing says that we can't enjoy other's Grandchildren.