According to this question by Diego ¿Quiénes serían los "piggybackers" y los "tailgaters"? the practice of carrying a child on your shoulders is called caballito in Spanish. To quote him
llevar a alguien a hombros o a caballito,
But the DLE definition states as its first definition
Juego para entretener a un niño, que consiste en sentarlo sobre las rodillas e imitar el trote o galope del caballo.
which unless I have misunderstood uses the word for knee not shoulders. Have I misunderstood the dictionary?
The reason I am interested is because I was trying to establish whether piggyback was a cultural universal as I am reviewing a scientific paper which uses it and I am interested in how widely it would be understood.