How hard was first grade for your child?

School starts in 2 weeks and I'm panicking. All year in kindergarten and now before school the teachers have been saying constantly how first grade is WAY harder than kindergarten. There are way more expectations and they need to pay attention and learn quickly because they have a ton to cover. How kids will fall behind extremely fast if they don't pick up on things right away. My son is one of the youngest in the class due to his summer birthday. In kindergarten they had to be able to read 100 words by the end of the year. I worked really hard at home and stuff too but my son was so stressed out and cried often because school overwhelmed him. He did well in the end but it was a lot.

I'm worried that 1st grade will send him over the edge with how they are making it out to be. Any advice? How did your kids do? We read everyday but if I'm honest I've been lax with math over the summer. I've been letting him be a kid.