My son has 100 invisible friends. They come with us everywhere in various numbers. Stinky recently made an appearance. He needed a bath although we couldn't smell him because he was invisible and he has an invisible smell. So I asked my son if he would give invisible stinky an invisible bath. He replied no because he has no invisible water. My son then made a trip to the invisible store to buy some invisible water.
Everyone who meets my son meets one or more of his invisible friends. We just need to be careful we don't sit on them or leave them outside.