I haven't been here for ages ... but here's my feedback
Amelia started school on 1 August (start of T3). The 1st two mornings went so well, even though leading up to her b'day, she'd not been looking forward to school, and had missed a school visit because of illness.
Because of (the same) illness, she had 3 and a half days off in the first week! Then another day and a half the following week. We then had about 2 weeks of crying every morning (for her) mostly just when I went to leave the classroom. She is now fine, and I hardly got a wave this morning as she was so busy!
So .. your start may be a bit rocky, but it'll get easier. Amelia's school is around 750 kids, so it's pretty big for a primary school.
If Isla does find things a bit hard going, we found inviting a classmate over after school, helped. Esp if they are feeling 'lonely' within the classroom. And talking to the teacher, with Isla, will help, if she thinks she is not doing so well as some of the other kids (telling her they've been there longer doesn't seem to matter).
Maybe get some rescue remedy for yourself. Personally, I found I wasn't looking forward to the whole school thing, but as it got closer & Amelia got more excited about it, I made that 'leap' into being pleased for her.