I took my child to Creston Park by bike during our last visit to Portland. Aside from a few issues (it was hot! and my kid wasn't used to their borrowed bike!) the ride there was mostly pleasant. We took some of the calm neighborhood streets and Greenways, and generally took a path along SE 34th, Clinton and SE 45th Ave. I knew we'd have to cross Powell at some point, but I guess I had hoped that there'd be a decent way to bike across it since Portland has relatively (for the USA) good bike infrastructure. I also figured that since there's a park with Creston Elementary school nearby, maybe the city would have made provisions for easier biking to school and play.
We saw another adult and children riding, presumably headed to the same destination, so asked if we could follow them for a bit. They took the 45th Ave pedestrian crossing across Powell and looked like they were going to walk down some steps (carrying bikes did not sound desirable for us) so we rode along the narrow sidewalk (with trees, poles, and a bus shelter interspersed) until we could cross Powell at 42nd Ave.
Waiting to cross Powell was kind of scary. There's not much of a buffer or shoulder at all between the sidewalk and automobiles driven at 40mph, so it feels extra scary being so close to the cars, especially when your kid still finds a way to trip over their bike every once in a while.
We waited for the light to change, and walked across Powell to 42nd. SE 42nd Ave near Creston Park in Southeast Portland has a full striped bike lane that felt like a bit of a relief, but still less comfortable than the streets north of Powell. SE 42nd Ave is a long, wide, and straight, with a large but unprotected bike lane. Maybe my worrying senses were heightened after crossing Powell, but I didn't really feel good at all riding with my kid on 42nd, I think mostly due to the speed of car traffic. She's pretty good riding in a straight line, but I'd feel a lot better if there were some physical barrier.
I researched this more later, according to PBOT and the Safe Routes to School map, there's no recommended (as in smiley-faced-Kid-safe) route to get to Creston from north of Powell. It was also later suggested that we could cross Powell, then take the path into the park from the NW corner at the stub of 43rd Ave.
Oh well. We made it to the park okay, and everything was great after we got to the playground and had some popsicles.