Wait until the baby ghast is fully spawned and not in the middle of an animation
Approach it carefully and keep your crosshair on the baby ghast
Use the interact/pick up action if the game version or mod allows it
If it is a hostile mob in vanilla Minecraft, you cannot pick it up
If you are using a mod, check that mod’s specific carry or capture item
Use a lead, bucket, cage, or special mod item if the mod provides one
Make sure your inventory has the required empty slot or item
Follow the mod’s pickup conditions, such as low health, small size, or calm state
If pickup still fails, verify that the baby ghast is actually meant to be carried in your version