I think children should be able to go anywhere as long as the parents are diligent. I've taken a 2 year old to the opera but booked a box so that I could manage any bad behaviour without upsetting punters who had paid lots of money to attend. Thankfully there were no incidents but had there been I would have removed the child pronto.
Personally I don't think pubs are the best environment for children but if you are going to eat that's ok.
If I was in your situation I would have taken the child outside straight away.
You're the adult in charge not a baby yourself waiting for your mum to come back.
