In honesty, I would go to a rescue every time. There are too many cats in the world as it is so for every cat you adopt out of rescue, you're actually saving two - the one you adopt, and the next one that the rescue then has space for.
If you talk to a rescue, they will be able to match a calm, friendly cat to you. If you definitely want a calm friendly cat, I would go for an adult aged 2 or over. It can be hard with kittens to tell what personality they will develop. If you want kittens, rescues also have plenty, but get two, they are company for each other and will play together meaning less behaviour issues for you to deal with if they need entertainment.
We actually got a calm, friendly mother from a rescue and one of her kittens which was a good mix. The kitten is 5 now and still slightly bonkers haha, very playful, a sweet personality but not as calm as her mum.
I also think with a two year old child, you are better with an adult cat ideally.
Other top tips - get insurance, have more than one litter tray, get some decent vertical scratching posts. Make sure you get them neutered/chipped/vaccinated. If you decide they are going to be indoor/outdoor cats, keep them in for at least 6 weeks before letting them out, and do it slowly and gradually at first. Always get them in overnight as night is when accidents are more likely to happen, and it reduces the amount of 'presents' you will get too. Look at cat proof fencing as a possible option (we have got this and it's fabulous - they can go outside but are safe).
Good luck and enjoy, we wouldn't be without ours :-)