My 6 month old had her first day on Tuesday (a shortened day as as first day)
I was terribly concerned she would sream the whole time and not eat etc
Turns out i worried over nothing - there was 30 seconds of tears and then ate lots and had 3 sleeps!
i had taken her for lots of little visits in the weeks leading up to it though which helped (and helped me more than her i am sure)
I know it is a bit harder with a 13 month old though so good luck and hopefully you are worrying for nothing