Check if card cost (on this instance of clone, or child of parent) is <= Mana, add this card to a list for the Enemy AI to use

trying to trigger an event so when the enemy turn starts, each card in the enemy’s had is added to a list if it’s individual cost is equal to or less then the current mana level… trying it from the current objects script, for each or etc

if (getComponent<CardStats>().cardCost <= battleStats.ManaThisTurn)
{list.add(cardID);

or 

foreach (transform child in transform)
if (GetComponent<CardsStats>();cards <= battleStats.ManathisTUrn()
{
{list.add(cardID);
}

If each card is a gameobject then you can give them a tag called card, and do something like this:

var cards = GameObject.FindGameObjectsWithTag("card");
var useableCards = new List<GameObject>();

foreach (var card in cards) {
     if (card.GetComponent<CardsStats>().cardCost <= battleStats.ManaThisTurn)
     {
          useableCards.Add(card);
     }
}