What does a bicycle call with two supporting wheel at the back?

Well, if it's an ordinary bicycle with two wheels added to the side, then those extra wheels are called trainer/training wheels. It's a so-so way of teaching people to ride bikes w/o falling over.

For kids they usually prolong the learning period, as kids tend to support themselves on the trainers all the time instead of merely having them as a stop when they're about to topple over.

the term stabilisers is also used in addition to trainer wheels or training wheels