Help!
Merry's just started barking at children and I'm not sure how best to handle it.
He used to be absolutely fine. He's only 6 months old but has definitely hit the scared phase I've read they go through (he's noticing a lot more than he used to and barking at anything that's unknown - plastic bags blowing about etc.). Do you think this might be the cause and he'll grow out of it or is it something I should be trying to train him out of?
About a month ago we met a lady in the park with 3 young girls, all of whom loved Merry and wanted to play with him - we were there for ages whilst they threw the ball for him and each time he fetched it for them and was a little angel

There's nothing I can put my finger on which has 'sparked' this - no scary incident that I've witnessed or anything. Our house backs on to a primary school and we also have 2 boys who live next door and are always out in the garden playing. He never barks at them unless their ball hits out fence or something, which is completely understandable.
It has escalated over the past week. This BH weekend we went to a pub with him and had lunch in the garden and tied him to the bench at our feet. It was extremely busy and packed with children. I thought twice about it but decided it would be another good experience for him. Every time a child ran past he went balistic, barking growling and throwing himself about

I could see the parents looking at us clearly thinking why had we brought him.
I told him off each time but none of the parents had the sense to keep their children away

I just don't know what to do. I am finding I am anxious when we see a child out on a walk now

This morning we met a lady with a little girl (only about 3 I think). Merry ran up towards them and I started calling him but he just ignored me. The mum was great and said they had 2 cockers at home. Merry was wary of the girl and was barking at her but also looked like he wanted to play. He was constantly wagging his tail and even started play bowing, but was still barking. Each time she walked towards him he ran away and even tried to hide behind me at one point.
So he seems to be better off the lead which makes me wonder if he was guarding us/ the table at the weekend??

Can anyone give me any advice on how to deal with this when we're out? I really don't want to have to put him on a lead and watch out for children all the time (almost impossible to avoid in this neighbourhood!). I'm also not sure how best to react myself - should I tell him off when he barks or reassure him?
I was thinking it would be great if I had somebody with a little one who he could get to know and then be ok with but I don't know anybody. I told next door about it and they said they used to have a cocker but had to get rid of him when they had the kids because he snapped at one of the children

I just don't know what to do because we would like to have children someday and I'd want to be certain that Merry would be fine with them.