I know my review of the 4T trail was negative, but fortunately I have a much better walk for your outdoor family experience. You can take a nice scenic loop along the Willamette River much more easily.
First of all, there is much better signage.
That is not specifically for the trail, but rather for nearby attractions and streets.
There actually can be some ambiguity for the route. I entered Tom McCall Waterfront Park from the Yamhill MAX stop, crossed on the Steel Bridge, went along the Eastbank Esplanade to the Hawthorne Bridge, and then went back to my starting point.
You can cross on the Burnside Bridge instead to shorten the route, although it is less convenient. I believe you can also keep going on for a while past the Steel Bridge.
You can definitely go past the Hawthorne Bridge to OMSI, and I believe cross on the Tillicum Crossing. I still believe it is easier to have all of those things be decisions and choices rather than getting lost.
I think this route is more scenic than the 4T in general, but also, I was interested to notice that for all of these empty moorings, the Portland Maritime Museum does actually use these lines to stay securely in their port. These are real working moorings!
Speaking of the Maritime Museum, this route also has many options for combining with other activities.
Not only are the Maritime Museum and Saturday Market right there, but you are also close to OMSI, as previously mentioned, and the departure point for the Portland Spirit. There are the various sections of the park, and the Oregon Convention Center which is also near the Oregon Rail Heritage Center.
There are rentals for bikes, scooters, and surrey style bikes, all of which passed me at one point or the other, but without any crowding or collisions.
There is also fishing, though it may be better to stick with catch and release. The sign seemed pretty discouraging.
It is also less steep than the 4T trail, which has its advantages.
I mean, I did find it more relaxing, but mainly I just found it prettier.
There is less landscaping along the East side, but they put in more art and that is interesting too.
There are also more places to obtain fresh water.
Here is the most important piece of advice I have for you, though it could easily not matter. As you reach the Hawthorne Bridge on the East side, you will see signs for the bus stops going East and going West. If you are catching a bus, pay attention, because you will not want to try crossing that busy street!
If you are just going over the bridge, following that signage can get you on the side of the bridge that matches the traffic flow, but the walkways are so wide it isn't a big deal.
Then you can take a stairway back into the park, or follow the ramp (with a nice walkway) into downtown Portland. It is safe for pedestrians (something not always considered with the 4T).
That is why I found this walking trail superior. However, if you want something more challenging, try the Wildwood Trail in Washington Park. (Although it is pretty easy to get lost there.)
Thank you Vera Katz and Tom McCall!