Jesus is talking to Pharisees. Pharisees is the symbol for literalism. Taking the Bible and the words to be of a literal meaning. Those “children” are people who are just starting to see Jesus represents consciousness and awakening.
So when someone starts to see Jesus is teaching consciousness and awakening, religious zealots who think he is literal and walked the earth and they have some believe system with rules like Judaism or Christianity or Islam or Catholics etc… they come along and teach that to the “little children” and lead them astray