https://www.youtube.com/watch?v=3yjWaobHbGs

the single collectibles are listed down below in the video describtion or here with some text.

optional collectible #1
Chapter: Young Apprentice
>> In the first chapter of the game just look to the left of your house up towards the treehouse.
Get the box with Daniels telekinesis and you have your first Item.

optional collectible #2
Chapter: The Gingerbread house
>> After you met your grandparents and slept over the first night, you come to a point where Claire leaves the house and you have to do the laundry. After that´s done go back upstairs and play with the train. Try to fully load his containers and let him drive through the tunnel. Make also sure that while you standing up the train is arriving at the station.

optional collectible #3
Chapter: Bending Laws
>> Pretty easy if you know where to find. Just get out and walk to the backyard of the Eriksons where the snowman stands. Look at him and then pick up your item.

optional collectible #4
Chapter: Bending Laws
>> Also pretty easy. Get into the house of the Eriksons, speaks to Chris and after some text you have to guess all the "Heroes" and "Villains" right. It is:
Heroes: Dino; Bear; Warrior; Pirate
Villains: Car; Insectiod
And voilà you get your reward

optional collectible #5
Chapter: Christmas Spirit
>> At the chrismas market go to the singer Cassidy talk to hear, wait until she leaves and at the spot where she was before should be now a litte present "belong to the girl".

optional collectible #6
Chapter: Screecing tires
>> The last chapter of the game brings you to the room of Karen. Just look at the CD Player, plug the cable and try to start it and you´ll get your last collectible.

Hope it helped some of you guys and have a great time play!

[You can ask if something is unintelligible]