Most of them couldn't, but I expect some can. 20 lbs is nearly as heavy as the 2-year-old herself. But the main limitations here are whether the girl can hold the item against her chest while carrying it, and whether she can keep her balance while carrying it. If she can manage those two things, probably she can carry 20 pounds.
And btw only males get hernias from heavy lifting.
And lifting something from the ground, bending over, makes it harder. If the girl can, for instance, pick up another child who is standing, and weighs 20 lbs, it would be almost easy.