As a child, I always knew something was off about me, and so did my parents. I lived and breathed androgyny (I didn't even know what it was back then), I played with barbies and hot wheels, things like that. There was still just something wrong about me. They figured I was going through my "tomboy phase" and I'd outgrow it once I got older. I really didn't care about my gender back then.
I hit puberty at age 10. That's when my life went downhill and I really began to care. I knew something was definitely wrong with my body, but I didn't know exactly what it was. I was diagnosed with Generalized Anxiety Disorder and depression. It was a very hard time in my life. I remember the numerous amounts of therapists I had, all of the medicines and such. At the time, I thought I had issues because I started going to a new and large school and didn't have anybody I knew in my class. Looking back on it now, that could have been a contributing issue, but I think the main reason I had such an awful time was because my brain was so traumatized by the female puberty that I didn't know how to react.
Before I knew I was trans, I was always told "The new changes are scary! You'll get used to it." and "You'll learn to love your boobs and curves eventually!" "Every girl hates their body at first!"
I remember constantly feeling the need to hide my breasts, and telling myself I'd get a breast reduction once I was old enough. I was dumbfounded as to how a woman could confidently wear a revealing shirt and not think twice about it. All of the shirts I wore showed absolutely no skin on my chest, which would constantly frustrate my mother, because most shirts in the women's section had v-necks, and "So what if some if only a little of your boobs show? It's not that big of a deal! Boys can handle themselves!"
To make a long story short, I ended up inheriting most of my shirts from my older brothers.
As puberty progressed, I didn't outgrow my tomboy phase. In fact, I became more masculine. I believe the reason for this is because as my body became more feminine, I tried to be more masculine to get rid of it. I hardly have a lick of femininity in me now. I like colorful things and little animals, but that's pretty much the end of my feminine side. I'm sure I'll become more feminine once I transition, but for now, I'm not.
So, is dysphoria always present in childhood? I don't think so. I'd probably be surprised if you said you didn't experience any, but if you didn't experience any dysphoria by puberty, I'd be really surprised.