Dog trainer/behaviour consultant here..
Dobermans (show bred, I would not entertain a working bred one if you paid me a million quid) will take a couple of YEARS to mature and reach the mental capacity to be fully trained.
Thats with bucket loads of time and patience, training and managing (people forget the management but it is key... preventing them practicing behaviours you don't like/won't like later on etc is vital or training simply will not work!), using positive reinforcment/negative punishment.
Please avoid any aversive, 'balanced', alpha, pack leader/dominance etc whatever bollocks, its all training via aversives and suppression which results in a potentially very dangerous dog no matter what the breed! It's also hugely popular on tiktok/reels and particularly within breeds like dobes, malis, rotties, bullbreeds, all the 'tough' breeds basically. Its nonsense, not necessary and not safe.)
With just a 7 year old, if you've the time and by that I mean one of you is home all day with time to manage and train the dog, and really, dog training/sports is something you're heavily into - yeah.
If you'll be relying on a dog sitter/walker/daycare, then think again - it will be the better part of a year before your dog can be left home alone for any useful period of time. Even if they are HAPPY with that (and most won't be reliably, usefully, until over a year old, sometimes more like over 2)... they will still not be suited to it, as its long periods of time where they can learn all sorts of things you absolutely do not want them to learn.
Imagine if you will, leaving a 15 year old boy home alone for a week, with his mates round, access to the booze cupboard and lots of cash. Thats the equivalent of leaving a juvenile dobe home alone for 4 hours. Chaos. Mayhem. Carnage.
However you're planning a baby - so you've to raise a steady dog who whilst still young, has to cope with a baby, who turns into a crawling poking grabbing wobbly noise maker... who then starts to toddle and stagger and grab and fall... and hit and poke and bite... and most dogs even if they were great with the small baby phase, struggle heavily with the crawling to properly mobile stage.
Juvenile dogs going through adolescence (which we now know takes the better part of a year, not a few weeks/months as many books suggest) are REALLY going to struggle with this, you'll need two pairs of hands and eyes in the back of your head just for the dog, which leaves what for the baby?
I would either...
Wait until the next baby is at least 5 (old enough to follow instruction and actually do as they're told)..
OR.. have the puppy, and don't start trying for a baby until the puppy is steady, trained, sensible and reliable, probably around 2.5 for a dobe.
Both together has the very real potential to be hell on wheels meaning you don't enjoy either dog or baby as much as you should, and the outcome for either is dire if things go seriously tits up with a big dog (and rehoming a dobe who has growled at or bitten a kid is nigh on impossible).