Hi
It does all seem so serious but lets remind ourselves (me included!) it is just reception and hopefully the start of a fun journey. My daughter starts this sept as well. Yikes!
Don't stress. My daughter is quite ahead of the curve so I'm concerned she'll get bored but the teachers I found out cater to all levels. The kids who are reading already will be given next level reading whilst those who don't know their phonetics or can't write their name will be taight from scratch.
Their goal is to prepare them for year 1 where, so I'm told, it starts getting academic.
Hopefully we can all let them enjoy reception and I'm sure the teachers will let you know if your child is really lagging behind and you can address that.
I think the above answers are all very useful so don't worry.