After the pool party and drinking beer with his friends, Elias and his girlfriend settle in to sleep for the night and Elias is wearing a light green T-shirt. In the next shot he awakens unsettled, and the shirt is gone. The shot after that has him on his bicycle at night, wearing the shirt again.
The grandfather decides to take his grandson for the weekend. He however has a dairy farm. It's impossible to leave a diary farm for a few days just like that; without extensive planning and finding replacement.