This is all a speculation, but I think it's worth considering the possibility that Ariel may have tried to go to the friend's school. I know he wouldn't have known where the friend is when he couldn't find him at home, but could it be possible that he may have had prior knowledge (perhaps from previous visits with friend) that the friend sometimes attends daycare at the school. The school is within walking distance to the friend's house. I am just trying to put myself in a 10-year-old's shoes who really wants to play with his friend.
Just a possibility/hypothesis worth considering for Montreal LE.
True, but for whatever reason he decided to go to the park rather than home. Two hours later he was spotted at the park, he may have gone directly to the park after learning that his plans fell through.
Here's a link to ice on the Prairies River in Montreal on April 9, 2017. It would be very easy for a child to mistakenly believe that walking on the ice was safe and to then go under the surface. The only evidence would be cracked ice near the shore, which is normal regardless of someone going into the water.
Bodies that go into icy rivers in the Fall or Winter are found in the Spring.
https://www.dreamstime.com/stock-ph...ing-des-prairies-river-montreal-image90466834