On our bridal table we had girl boy girl boy etc.
I would be pretty annoyed if I was unable to bring my 4 month old daughter to a wedding I was invited to. Its just that I am breastfeeding and I would prefer to have her with me than with someone else. At the moment, the only people I trust to look after her is family, and I'm assuming if its a fmaily wedding, then all those people will be at the wedding.. kwim?
I also agree - once the invitation are out, no more guests!! I would just say something like 'sorry we've already sent out the invitations and booked/confirmed the restaurant and cant add any more guests". If you havent sent out the invitations and she wants to bring him, then I would invite him.
We invited about 70 guests, and only one did not come. Most people will come to a wedding.