The best way to find out is to have two toy cars. Then add some mass to one of them. For example, you could tape coins to the car. Then line them up side-by-side and use a pencil or ruler to apply the same force to both of them. Again, just give them a tap. Which one goes faster? You probably found that the one without the added mass sped up more.

That is, for the same force, the greater the mass, the less the acceleration.