My family has been to Aulani three times since reopening (Nov, Dec, and April) and this has been our experience. The water slides are open and our experience was that people were good about spacing themselves out. The chairs are socially distanced and you'll be fine while lounging around.
The Menehune playground is open, but it's nearly impossible for the kids to socially distance because the pathways are only 4'-5' wide. However, nobody is standing still for very long and all contact is extremely brief.
The lazy river can sometimes get congested, but you can pull over to the side and wait for people to pass.
The jacuzzis and the edge of the grotto pool overlooking the lagoon can get overly crowded at time imo. The rest of the pools felt comfortable, and we had no problem distancing. If some parts of the resort get too crowded, you can always find an area where you are more comfortable.
I have a 2yo and 5yo so I certainly understand your concerns. For peace of mind, I kept reminding myself that nearly everyone around us had recently tested negative and Hawaii has some of the lowest covid numbers in the US. Also, most of the Hawaii covid cases have been linked to clusters and contained. I felt the benefits of being out of the house, enjoying family time (as if we didn't have enough of that last year lol) were worth the risks.