Dek Ai' has his own rules putting the cars in groups. That big red van with that the yellow sporty one. The red, green and yellow small ones with other small cars. And those last four in a row.
Can you see the rules for the last four? They are various in shapes and colors. So what the similarity? They were bought in one set. Yes he remembers that.
He still have one other group of buses and train, and a group of big sedans. He only plays one group at a time.
You may wonder why I pour him with so many toy cars. Well you bet. I pour him with things much more than I gave to his siblings. Not because I love him more than the others. I love them all the same. It's just that Dek Ai' needs more specific stimulants to learn things. And as I still haven't found that specific thing, all I can do is give him as much as I can.
I hope that will work.