My sister and brother-in-law in the Netherlands have a similar situation with a 3 month old and 3 year old. She uses a bakfiets cargo trike to haul both of them to school/daycare/store etc. I hear that there is now a bakfiets dealer in Portland, but cannot confirm. I have no experience with either product, but the style of the weeride is very popular for transporting children in the NL.

I know you already said you weren't thrilled about a trailer, but just to throw it out there: The trailers really are very easy/quick to remove and I wonder if your daycare provider has a place for you to store it/lock it up there.

Either way, good luck and good for you for sticking with your bicycle commute.