@billyli My daughter isn't in school yet. She's almost 2 and we'll put her in prek at 4. However, your son is used to school and enjoys it so I would lean into that. It will make him happy to still go and make your day a little easier with an infant at home. It would be totally fine to delay putting your youngest in school. As other people mentioned, under 3, it's not going to make a huge difference to them.
I just recently became a SAHM and my decision was driven by our schedules. My husband is in school, works overnights but does a 4x10 schedule which often turns into 4×12's. He wasn't getting much sleep, I ran out of sick time early in the year due to illness and I was already working PT.
Now we have more time as a family, dinner time is easier, if our daughter gets sick there's no stressing over who calls out and whether we'll get reprimanded, etc. It was the better option for our family. If you can afford it, and you don't love your job and will feel lost without your career, go for it. You can always leave on good terms and see if you can go back if it isn't working for you. And there are always other jobs if not.
I'm able to actually stay on top of the house, bring her to activities/get outside more, focus on my degree & take care of myself better being a SAHM. No regrets so far.