Hi Rachie
Dogs and children both benefit from being socialised around each other but ideally you'd try and match a very young child who has little experience of dogs with an older bombproof dog and vice versa.
I must admit I'm in favour of
ignore with very young children. My dogs are introduced to the room when the littlies are completely occupied doing something else. I've never really encouraged my nieces and nephews to interract with the dogs either. I've found that both kids and dogs settle down very quickly in each others company and don't need formal introductions.
I would also not introduce treats from children either. I don't want my dogs to see the kids as a source of food, particularly as any food they carry is at nose height and easily snatchable. Feeding the dogs brings a level of responsibility the children just aren't capable of and an excited, food motivated, dog is a hazard. Visions of baby skittles comes to mind!!
Your doberman is communicating discomfort and that's completely ok. A tottery 2.5 yr old heading towards him might look a bit alarming so I'd concentrate on no touching, no talking, no eye contact. Distract your neice and keep her busy, and away from the dog and he'll probably potter over for a look sooner or later. If you want to introduce him to the sight, sound and smell of kids he can sit by the play areas in the park for a non threatening, non interactive look-see. Proper meetings can come later

As a general point it's worth mentioning that children
should learn to be wary of dogs - not frightened, but cautious, and careful. Not all dogs are ok to touch and many dogs can be unsettled by children. Better that she learns to respect unknown dogs and luckily she'll have you to teach her how to behave around them.
Kindness is the language which the deaf can hear and the blind can see ~Mark Twain