So I was re-watching and reading Dragon Ball some time ago and I started to think, why these two little boys were able to turn into Super Saiyans so easily and so young and Gohan had to struggle so much even though they all are half-saiyans. I came up a theory that it might have something to do with the fact that when Gohan was born Goku was not able to turn Super Saiyan then, but when Vegeta's and Goku's wives had given birth to Gohan and Trunks, Goku and Vegeta were already able to turn Super Saiyans.

So what I'm trying to say here is that maybe because of that those two kids had some of the Super Saiyan genes in them (if that's even the right term) and they are so pure of heart and full of joy, just like Goku was when he was a kid. So it feels so natural them to transform, just like they were in the hyperbolic time chamber where they learned to turn Super Saiyan 3 when fused, and they only saw Goku doing it twice (in comic he did it only once, but anyway..) And also another theory is that because they are half-bloods so maybe the human genes has something to do with this.

Not sure about this, so what do you think about this? Or what is your theory about it?

It's interesting because I have always wondered why it was so easy for them to transform while vegeta and goku transformed either when their friends died or they were just filled with strong emotions, meanwhile trunks and goten achieve it like its nothing. Gohan, Goku and Vegeta all were motivated and had to train very hard in order to become a super saiyan and achieve ascended status in the hyperbolic time chamber. I think it might just be because both goten and trunks were conceived after their fathers could become SS with ease. Because by the time Goten was born, Goku could already become one pretty easily, so I guess he just passed the gene down to Goten, therefore, he didn't need as much emotional motivation to attain super saiyan because his father already passed that ability to him before he was born. I also think it is because they are hybrid half saiyans rather than pure super saiyans like Goku and Vegeta. But that's just my theory...its not fair though because the other saiyans actually had to train and pushed to their limits to get SS, and these two are able to achieve it like nothing...oh well, it's not my writing XD

Razor-987 : Don't think it's very fair either.. But can't figure out  any better ideas why they were able to do it. :p

I too feel the same way.....I mean goku himself along with gohan and vegeta had it pretty ruff time when ascending to SSJ form. I think its a bit unfair that those two can do it with ease....but, they did have a tough time when going SSJ3 though. So in a way they got their fair share of feeling how hard it is to ascend.