However, most likely your going to be stuck between a rock and place and will have to endure the procedure. Maybe, sending your fiancee to do most of the paperwork and enter the pin, whils’t you look after child and swop over, whils’t you take delivery of the car and sign the driver decleration may help.
This might actually be the best option.
Have your fiancee go with her mum, let her do all the paperwork etc while you stay at home. Ask the salesman to park the car on the customer parking lot. After all is filled out and the car is yours, have your fiancee come back and watch the kid while you go and pick up the car off the parking lot.
If you’re reasonably competent, you won’t be bathled by a new car – all the setup etc can be done in peace at home, manual in hand if necessary.
Prior: SEAT Ateca Xcellence Lux 1.5 TSI DSG MY19, VW Golf GTE PHEV DSG MY23
Current: Hyundai Ioniq 6 Ultimate
Next: we'll see what's available in 2028.