Is being too perceptive at a young age a good thing?

My nephew's four-years-old (almost five) and I love as if he were the little brother I never had (I'm sixteen, by the way). He's a smart kid and he's very witty for a kid his age. However, I'm not sure if he's a little too smart for his age.

My brother and his family came to visit for the 4th of July. We had a conversation about the kids. From what I was told, my step-niece's father lives about ten minutes away from where they live (my brother's in the Marines) so he's able to see her whenever he wants and they Face-Time everyday.

Here's where my nephew's mother comes into play: She doesn't attempt to call him and see how he's doing. Apparently, she just sends texts and makes up half-*** excuses and inconveniences about why she couldn't visit him. The only time she visits is when they come over to my home.

Anyways, my nephew has definitely noticed something's up. I can imagine that when he sees his step-sister talking with her father on her iPad, he's probably thinking 'When's it going to be my turn?' or 'Where's my mommy?'. Don't get me wrong. My nephew is a very happy kid but sometimes he'll just burst out crying and say things like 'I miss my mommy'. (Keep in mind that me and my family aren't exactly on good terms with his mom anymore).

So, there's the story. My question: Is there something that we all should be doing? I know he's young, but I'm not asking about something that could be traumatizing for a kid his age.
Added (1). Just a little something to consider as you think of an answer: My older brother has gotten a divorced and remarried a nice woman. They both have kids of their own, my nephew (four-years-old going on five) and my step-niece (a year older). As of five months ago, my brother's new wife had just given birth to their daughter.

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