DD1 (now Y5) was an autumn birth and made this transition with no bother. DD2 is a summer birth and has just started in Y1 with a few grumbles.
They had started the transition in the last term of Reception so she was prepared to an extent, and she is enjoying it, but she says there is too much 'learning'. Reading practice books are coming home as they did in YR, but homework will start soon (online maths, spellings and learning log projects), and I'll need to make this seem as fun as I can.
There seems to be a lot more pressure in Y1 than there was when DD1 was there, with the phonics check and the increasingly raised bar from Mr Gove.
I do see a lot of positives though. She has never been much of a talker, but her conversation skills have improved markedly in the last week. Everyone is noticing this, not just me. She is actually less tired after school, strangely since the work is increasing. She is taking more of an interest in the after school clubs, but this is probably more due to the fact that more are offered when they get to Y1.
It's early days yet in the term, and my advice would be to keep positive about it. We all panic occasionally about our children and the time of year they were born makes a big difference when they are small but they all get there in the end.