Much of what I would say has already been said...
So just reiterating getting two kittens is definitely better than one, they will grow up much happier and better socialised and cause less havoc.
Although I would possibly recommend you consider a young adult rescue rather than kittens - a laid back, child-friendly cat, around 1-5 years old. You will know their personality much better, kittens are a gamble...
They do create some "mess" in the home, there's no getting around that. Some tracking of cat litter, or bits from the garden if they go out, cat hair of course on soft furnishings and your clothes... On the other hand cats are very clean and with kids you are probably already used to some "mess" and maybe clean regularly enough to not notice any extra?
Other things to consider - finances (insurance, annual vaccinations, monthly flea and worming treatments, food, litter, bigger purchases like carrier, cat tree, toys, bowls) and arrangements for holidays.
Also your location - busy roads? Detached house with easy access to front or a terrace with a safer network of gardens at the back? Would consider you catproofing your garden or getting a catio built (safety for cats + less chance of "presents")?
I love having cats and wouldn't be without but I don't have kids and mostly work from home so really appreciate the company.