OP, I don't think you will be mistaken for Grandma! Especially since you still have little kids, I mean if you're out somewhere with 4 yo and baby, no one will think you're the baby's grandma and the kid's mom.
I have 20 something kids (and a teen) and a 5yo. The only time I have ever been mistaken for grandma was when we were at a restaurant with adult dd and ds and the baby was 2-the waitress thought they were the parents, which is understandable!
Not going to lie though-my 'peers' all pretty much have grown kids and even grandkids. I have some young mom friends and I like their energy. I have one friend who is my age and her dd is same age (she had a long fertility battle) and we relate.
I will indeed be the oldest mom in her K class next fall. That's ok

I'm sure some young moms think it's weird. That's ok too! They'll understand in about 20 years LOL.