At least 80cm to 1m wider and longer than table will allow chairs to be pulled out etc without rucking up carpet. Your local carpet shop should be able to cut you a remnant or off cut to size and have the edges whipped to form a rug.

I have an old 1930's table which is square and can fold out to rectangle when needed - some may think it looks ugly but I've grown to love it!

Can you please draw out this room plan and add measurements, I can create a layout for you from this, thanks. (and Good luck with the little one!)

Depends on the size of the room, it’s shape, and size of the table. I changed my kitchen table from a square with high backed chairs to a slim rectangular table with chairs with a low back, and it looks much better and gives us more space around it.