Hello & welcome
@novice2023
I
hate being this guy but I'm going to be.....
From your other post......
I live in London (UK). I am not a good cyclist and do not know much about bikes.
Lots of people carry their kids on bikes, sometimes more than one kid at a time but I'd venture not many start off from where you're starting from.
I hope you get lots of responses here but if not, I'd suggest doing some more (in fact, a whole lot more) research before buying a bike.
I'd imagine there's a lot of Facebook groups and probably websites dedicated to what you want to do.
YouTube could well be your friend too.
Keep your eyes open at schools and see if you can spot and talk to others who do what you want to do.
Maybe ask in the school your child attends to see if anyone else is doing this? Maybe you can have a chat.
Shops that sell child seats may be helpful too.
In the meantime, beg, borrow, or use a Borisbike and get out there so that you become a better cyclist than you are now.
So much of cycling safely, especially in a city, is based on experience. Perhaps look into any cycle training that may be available. (Cue incoming abuse

)
Build up your confidence and skills then attempt the school run at the appropriate times. See how it feels.
Don't forget, you're going to have a 16kg, very valuable load propped up high that's going to make cycling less stable.
No harm to give them lots of practice too in advance of hitting rush hour traffic. The calmer they ate the safer you both are.
Other things to consider are weather (and what to wear), lighting and basic maintenance such as punctures.
Also routing. The way you currently go may not be the most bike friendly.
Presumably you have a safe and secure place to store the bike?
I used to live in the Netherlands and kids as passengers on bikes were as common as muck. However, there is an excellent cycling infrastructure there.
Cargo bikes as multi-purpose machines were quite common. As many as 4 kids in the "cargo space" for the school run, buy also used for grocery shopping, errands and days out. A lot more expensive than your budget, requiring more storage space but an investment more than an expense giving the opportunity to save on car running costs and/or public transport.
I hate that the tone of my reply may be seen as negative but I think it's (almost) vital for safety, success and enjoyment that you have a good think about this, get some practice and skills under your belt and start off with your absolutely best foot forward.
TLDR?
If your only choice is those two go with the
Decathlon bike.