There's not much that can be done for the few sticky spots on the way to the science hut (I've lost collectibles that way myself...) but as bajantara says, with practice you can learn were there are "safe" places to pick up a kid. I usually place him/her a little bit away from the collectible towards the hut and that usually works, especially for the sticky spots near the ocean or on the mosaic.

Another thing to watch for is that if you already have one kid on his/her way with a collectible and you spot another immediately, wait until the first one is deposited in the hut, otherwise it'll get lost. (Or if the second one is that rare collectible you've been waiting for, you may be willing to let the first be dropped to make sure you get the new item.

As for the frequency, it may just be that in a second game you aren't watching it as often as the first time you played and it just seems that they show up less frequently. Or a diffeent order of tech upgrades can make a difference.

In a new game I recently started, I got very lucky and my first event gave me L2 Explore! I only have 8 villagers, just harvested my third crops, still clearing the briar patch, but I already found all of the shells, 9 butterflies and 8 pebbles!