Air Child - attacks target creature, when this skill is used, air child does not attack opponent this turn
Earth Child - burrow, target creature is now burrow (cannot be tageted but losses half their attack) and losses air borne
Water Child - turns target non shield, non weapon permanent into a water pillar
Gravity Child - +1/+1 for every gravity pillar the player controls
Child of Life - +1/+1 for every creature the player controls
Fire Child - 1 damage to target, if death results from this skill, +1/+1 to Fire Child
Child of Light - instead of attacking, uses attack to heal controller
Child of Darkness - +1/+1 every time it damages the opponent
Entropy's Child (or Chaos Child, or Child of Chaos, whatever you think sounds cooler) - X/y+1, the attack and health of this creature changes each turn from 0-5/0-4
Child of Time - cause opponent to put a random card from their hand back into their deck
Aether's Child - cause target creature to phase out 2 turns, phase out creature cannot be targeted and cannot attack or use its skill
Child of Death - hex target creature, when hexed creature dies, it's controller suffers poison damage equal to the creature's casting cost
The upgraded version will be a "Champion". Just substitute "Child" with "Champion" and keep the same casting cost but increase base stats.
If you don't like "Child" and "Champion" you can always use "Spawn" and "Beast", or "Sprite" and "Spirit", or even "cherub" and "seraph"