Since FNAF and Walten Files are similar, I thought of this. 

What if Chica and Duckie were related at some point? (BEFORE YOU START YELLING AT ME ABOUT THE SPECIES DIFFERENCE LEMME EXPLAIN-)

Duckie was originally human and his name was Porter and so were his parents and Suzie (Chica). 

It was until Duckie gained the ability to morph into a duck to get himself out of trouble. 

On the day Suzie (Chica) was killed, Porter (Duckie) was merely a few months old so he has NO memory of her at all. Heck, he thought he was an only child. 

It was until Tammy got the job at Freddy's and she thought the animatronics moving on their own was a nightmare since she dozed off but jolted awake. 

Time went by and Duckie was starting to get a familiar feeling about the animatronics including Chica but shrugs it off anyway. 

I know this is VERY confusing but I feel like it would make sense. 

Duckie and Chica almost sound the same except Duckie sounds more masculine while Chica sounds more feminine. 

And for Duckie's cautious behavior was caused by Alice (his mom) being so over protective of him ever since Chica's death.