Three youths have been charged with motor vehicle stealing in relation to the death of pregnant Hobart mother Sarah Paino.

Ms Paino, 24, died in January after a four-wheel drive being driven at high speed collided with her car in the Hobart CBD.

She was on her way home after dropping off her partner Daniel Stirling at work for his night shift.

The car that struck her was being driven at speed by a 15-year-old boy.

He remains in custody after being charged with manslaughter and motor vehicle theft.

The three passengers in the car, a 15-year-old boy and two girls aged 12 and 15, have now been charged with motor vehicle theft.

The charges come after police determined there was "no reasonable prospect of conviction in relation to more serious charges".

Ms Paino was 32 weeks pregnant at the time of the crash but doctors were still able to deliver her son, Caleb.

Her two-year-old son Jordan was in the car but escaped injury.

Since the crash, more than $500,000 has been raised to help Ms Paino's family.