I am not sure it was the fact that you didn't want to cuddle the new baby that made people call you a heartless bitch.
It is a pity to put your own reaction to babies ahead of the bigger picture here. Visiting the new parents is an act of support for the mum especially, who has probably been through a life changing experience, painful, and even traumatic. After all that, it is nice for the parents, especially the mum, to be told her baby is gorgeous, looks so healthy, the mum herself is glowing, must feel so proud and happy, etc... Surely it wouldn't have killed you to go to visit, maybe bring a casserole or a bowl of fruit, and be nice to a new mum for a few hours?
Likewise, suck up the performing pony children you are faced with. Feel sad for them that their parents see fit to put them through such cringe-making experiences with others watching. Then congratulate the parents on their lovely children, and move on with your life. That is all the parents want.
A little thought of others goes a long way.
In real life people just seem so aghast at the idea of me not liking them and we don't really get any further than that.
Clearly you have told people that you don't like children, then.
Why?
Are you seeking some sort of attention? You know it will focus attention onto yourself, and you have gathered that the attention will take the form of disapproval. Do you have to wear your heart on your sleeve to that extent?
I accept children are people but obviously they are very young people who I have zero in common with and I guess I miss the point in putting effort into getting to know them because it seems entirely pointless to me. What are we going to talk about? And that's if they can talk! The stranger children approaching me in the coffee shop, what am I supposed to say? "Hello, terrible weather we're having isn't it?" That would be my normal approach to a stranger but doing that to a child would result in them staring blankly at me. I just can't do the whole 'hello, how old are you then?' '5'... now what?
You are not necessarily put off by the possibility that you and strangers might have nothing in common. You approach them with a comment about the weather. You are expecting a response in similar vein/tone.
You are very nervous that a child will leave you dangling and feeling stupid. Maybe you like to feel in control of situations.
If a child you do not know comes up to you in a cafe and appears to be trying to make contact or is just staring at you, how about asking where their grown up is and when they point or tell you, then tell them to go back to them. Or you can wave at the accompanying adult and cheerfully tell them their little one has strayed. It's not a sin to want to drink your coffee in peace and not entertain some random child. Take control of the situation, politely. The accompanying adult may get your gentle hint.
What you need is assertiveness training.