I would do 2 or 4.

My friend was in this same situation. She invited her preschool class and new class on the first week of school. I think it was Labor Day weekend so she had the party at her house on a Wednesday or Thursday. There were some people who were invited on the day of the party. Weather was nice and it was a backyard party.

Just invite his preschool friends and have it before school starts.

Nobody give a shit. Relax have a drink.

I vote for #4 emphatically. 5 year olds don't need or care about big parties.

End of September with everyone in his class invited

We have this and I normally send the invites the day the class list comes out. I invite everyone and plan the party in advance for late Aug/early Sept. It works out great as I get to know the parents better too. Now my child is in 4th and this year he said he doesn't want a big party, so we'll do something else with just family.

My kids have an early September and early October birthday and each of them has done some version of the whole class party early in the school year, and it’s been great.

For my DS with the early Sept birthday, when we were in a situation like this (except it was moving to a new school for pre-K), we did the small party in early august with preschool friends and I ended up regretting it. It was a lot of work and money for a party that few kids ended up being able to attend (it felt like 80% of invitees were in OBX that week) and with kids he has barely seen since then. For the next year, transitioning into K from pre-K, we did a whole class party on the second weekend of school. Literally every kid in the class came and it was a great way to meet new families.

4 or 2. I think it’s really important to get to know the school community, so my own preference would be for the October party. At that age, you’ll meet parents and get to know his classmates.

Most kids aren’t having a big bounce house type party every year. Invite a few friends for an outing or have a family party, he will be just fine.

We were in the same situation a few years ago. I did #4 because my son didn't want a big party. BUT I can see a lot of benefits of #2 if it's short, and low-key, it's a great way especially at that age for you to meet parents and help facilitate friendships.

Depends on your kid and what he wants. One of my kids has a summer birthday and is pretty shy. She much prefers to coordinate a special activity with one or two close friends. She would be really uncomfortable with a bunch of people she met the month before. My other kids is a total extrovert who loves parties - she has a spring birthday and always wants to invite the whole class. For her the later party with everyone she has ever met would be the winner.

Maybe you could do a combo of 2 and 4? A birthday play date with a couple of preschool besties and cake close to his actual birthday, and then invite the whole class to a playground or something low key in October? As a parent, I appreciated the whole class K parties early in the year because I got to meet other parents. But that’s only if the birthday kid is up for it!