If these are two seperate tickets, you have no chance of making it.
If this is a single ticket, it's doable but tight. Your best shot is probably to take the Aero Train. https://www.flydulles.com/iad/aerotrain-washington-dulles-international-airport
Unfortuantely there is no stop in Terminal D, so on arrival you need to hike all the way to the end of Terminal C and take the Train and exit at Terminal B. The train has level entry/exit, but you will probably need to take elevators to get up/down from/to the train level. Good news: you don't need to go through secuirty again.
Some tips & tricks
- Minimize the stuff you carry on. Lugging a a large roll-aboard carry together while pushing a stroller will slow you down and be awkward.
- Familiarize yourself with the Terminal. Have a map ready on your phone
- Make sure you know your arrival and departure gate in Dulles. These should be displayed on your barding passes but you can also check flight status online for gate info. Make sure you know how to do this: practice the day before
- Map out the route using gate info and map. Signage is not always the greatest. Walk from Terminal D towards terminal C, make ure gate numbers on D are dercreasing. Entry to the train is between gates C14 and C18 , etc.
- Tell the flight attendent that you have a tight connection. If you are lucky, they bring up your stroller first.
The stroller is not helping. If you want to carry it on, you can drop it off at the airplane door on departure, but on arrival you need to wait at the airplane door until it's brought back up from the cargo hold. You can potentially check it through to your final destination, but then you will have to carry your child for the entire connection and you will only get it back at the baggage claim in Europe.
One more tip: make sure you have the apps downloaded for all airlines involved. Make sure you have accounts are logged in and have the confirmation code for each ariline handy or already stored. Since it's Dulles, it's probably a United ticket: the United app has a very good feature called "Connection Summary" that tells you exactly where you arrive, where you depart, and how much time you have.