This is a simple permutation and combination problem. Because of the arrangement of symbols, the formula is not easy to write, which is roughly expressed as follows:

C63 times {A33}= 120

C63 refers to choosing three children from six children, without arrangement, only choice, where 6 is the lower foot mark of C and 3 is the upper corner mark of C; {A33} It means to arrange three children in three different chairs, one is the lower foot sign and the other is the upper corner sign.