Rosa, I definitely agree about kids needing their space, but there's no need to get too fussy when it comes to a baby - for years and years there wasn't even such a thing as a BABY room, kids only got their own room as toddlers, infants had a crib in the parents' bedroom. I'm not talking about the dim dark days of history, or even about poor families where pretty much everyone slept in the same room, just about a time of differing infant rearing practices.
In the example of the transformers, I think it's more than likely that by the time the kid is old enough to have a mind of his own, the dad will have moved on from the collection. Even if he hasn't, the kid will probably be conditioned to like these already, having grown up looking at them. Later on he might not, but all that's needed there is a bit of sensitivity on the part of the parents to listen to what their kid needs. I don't know just what kind of space we are looking at here (that the collection would take up) but with this type of thing, where it took time and effort to bring these items together and it's something deliberate as opposed to random pack-ratting, I don't think there's any reason to just get rid of it immediately.
Frankly that thing about selling the transformers kind of reminds me of that ancient Julianne Moore/Hugh Grant rom com, Nine Months, where as soon as the woman finds out she's pregnant, (unplanned), suddenly she goes from poised, independent woman to clingy, whiny 'little lady' type and demands that the guy toss out his beloved, elderly cat, replace his equally beloved kick-ass sports car with a 'family car' (as if - I rode EASILY in the backseat of my dad's sports car 'til I was five, and I was VERY tall for my age) and accompany her on endless cooing shopping trips for baby items - basically, just shed everything that mattered to him, right then and there, in the name of proving some elusive 'commitment'. The audience is clearly meant to be on her side and feel for her that her man is so immature, but I've always rolled my eyes at that lol