I took the kids to Mt. Scott Community Center in SE Portland a couple weeks ago for open swim hours. The weekday "family swim" hours are not exactly ideal with nap time schedules, but I figured I would try to make it work. Open swim goes from 11:30am - 1:00pm. The cost was extremely reasonable because I only had to pay $5.50 for myself. Kids under 3 swim for free.
I knew I wouldn't be able to manage two very little non-swimmers in a pool by myself so I enlisted some help. My sister-in-law came with her daughter and my father-in-law came as well. I did not consider the locker room logistics of getting two kids ready to swim and also getting us all showered and dressed after the fact on my own though. That was rough, but we got through it.
It was relatively busy, but not packed. I didn't feel stressed out about the number of kids there. The pool is set up perfectly for families with kids of all ages. There are plenty of shallow areas where both kids could reach the bottom. Pearl was able to walk around a lot. There is a fun, colorful area with lots of spraying water that the kids liked to play in.
They had plenty of foam kick boards available for anyone who wanted to use them. There is a current area for floating and the kids enjoyed us taking them through on the kick boards. That area was mostly full of older kids as school wasn't in session that day, but we didn't have much trouble maneuvering through them. They were thankfully all well behaved.
By the end of open swim, the kids were tired and starting to melt down a bit. Pearl especially had fun though and didn't want to leave. It was also an added bonus that both of them had great naps after all of that activity.
I absolutely recommend Mt. Scott Community Center. I hear there are other similar community centers in the area worth checking out too. My only warning is that if you have more than one kid, enlist help. You will need it.