Toddler has developed fears

It could be related to an experience that he went through somewhere, or witnessed happening. While growing up (even till now), I have a fear of not having the main door and gate locked - always checking several times whether it's been locked and being the one to close it has always been my most feared thing - because my grandma used to misplace our keys a lot, a couple of times it was near our unit or even from the door. That was how I developed the fear and while it doesn't happen so often now, sometimes I'd still get nightmares about people trying to break into our house! It could likely be something he came across in school, an advertisement somewhere, a children song with a video of mouses entering people's homes or noticing a mouse somewhere else - kids notice a lot more things than we do, including our surroundings and their parents' feelings! Having said that, I think it's something you have to address and help him get through the fear. If he is able to express his thoughts (since you mentioned that he thinks it's a mouse), you can carry him to the source of the strange noises and show it to him so that he's not as afraid after he knows what it is :) My son is afraid of sudden, loud noises that he cannot identify - but if I stay calm, keep him in my arms and within safe distance and explain it to him calmly then he'll understand it's not something to be afraid of :) While it wasn't triggered by anything, it's likely that it's just part of growing up where they start developing fears - and that's where we come in to help them understand things that aren't as scary as they think!

i helped mine to overcome by being friends with the thing. mine started to develop fear for cats. i told her how the cat feels and cat would love her to be gentle. i also told her that the cat can be her friend. she talks to the cat and said hi. soon, the second time, she took initiative to say hi friend. and she was over it. anything can make them cry in midnight. being too excited or even a documentary before mine sleeps. she woke up crying. but 2yo, there will be a period for night terror

play a game with him, you can try 'Going on a Bear Hunt' with actions and song along the corridor, and leave a teddy bear at the end of the song in a box behund the door and let him find it. it's fun and not scary at all. this way he can learn that his fear was not real. hope it helps

Is it due to some tv shows? coz sometimes some shows that they watch can traumatised them too.

There are nightmares as well...