Pendelhaven Elder's ability affects only 1/1 creatures you control at the time it resolves. Creatures you begin to control later in the turn or that become 1/1 later in the turn won't get +1/+2.

Pendelhaven Elder's ability looks at each creature's actual power and toughness taking into account counters and effects that raise or lower its power and/or toughness, not just its base power and toughness.