Ehhhhh, I can't say I'm particularly on board with how many assumptions that'd have to make about each Inquisitor. Nor am I particularly fond of the idea of playing a child. I found it awkward when it happened in the beginning of The Last of Us, and that's not even really a roleplaying game; I'd find it rather uncomfortable to be expected to take on the role of a child - especially in a world as messed up as the Dragon Age 'verse - in an RPG, even if it wasn't for much more than a brief intro/prologue.
But back to my point: Personally, my mage Inquisitor would use her magic to destroy anyone who dared try to take her child away, even if that person was the King or Queen themself. And I can't imagine she and Cullen wouldn't be able to convince everyone that their child is perfectly safe and in good hands. After all, said child would have a Templar-trained father to guide them and highly-skilled mage mother to teach them. It's like their own, little Family Circle. It'd tick me off if I had a specific course of events rammed down my throat, dictating to me how my Inquisitor acted without my actual input. I didn't put over two hundred hours into her just to have her personality and strengths (and the fact I actually don't want her future to include children) completely ignored in favour of a railroad path.
Also, just imagine all the other couples, both gay and straight, and all the different personalities for Inquisitors beyond what the game can properly track. And those who didn't pursue romance options. They developers would have to waste a metric ton of resources better put forth to other elements of the game just to account for all the possible histories, families, and outcomes.
Not that it isn't a great idea for some -- in fact, as a fanfic or something, I'd probably enjoy the premise -- it just isn't a thing I'd like to play and it'd pose so many issues for the game designers and writers. And the artists, I imagine, as they'd have to account for every potential race combination as a child when designing the attire -- even if we'd be locked into one outfit (think: Skyhold Jammies) during the childhood portion.