Matthew 21:12-17

12 And Jesus entered the temple and drove out all who sold and bought in the temple, and he overturned the tables of the money-changers and the seats of those who sold pigeons. 13 He said to them, “It is written, ‘My house shall be called a house of prayer,’ but you make it a den of robbers.”

14 And the blind and the lame came to him in the temple, and he healed them. 15 But when the chief priests and the scribes saw the wonderful things that he did, and the children crying out in the temple, “Hosanna to the Son of David!” they were indignant, 16 and they said to him, “Do you hear what these are saying?” And Jesus said to them, “Yes; have you never read,

“ ‘Out of the mouth of infants and nursing babies
you have prepared praise’?”

17 And leaving them, he went out of the city to Bethany and lodged there.

The reason there were moneychangers and merchants in the temple courts in Jerusalem was so that pilgrims who came in from far away could easily buy an animal for sacrifice. Galilee is in the north of Israel, e.g., and I'm told it was at least a two week walk from there to Jerusalem. Obviously, it wasn't practical for Jews coming to worship and sacrifice in Jerusalem to bring animals with them, and the Jews of the Diaspora wouldn't even have the appropriate currency with them, hence the need for the moneychangers.

So, I don't think it is the presence of the moneychangers and the merchants that is necessarily wrong; it is their abuse of their position to which Jesus is objecting. If they had offered a fair rate of exchange and fair prices, then they would have been doing the pilgrims a service. But, it seems they were price-gouging, and thereby profaning the Temple.

P.S. Unlike the adults, the children in Jerusalem understand who Jesus is.

P.P.S. The overturning of the tables in the Temple courts is a profoundly provocative act, and one that leads directly to Jesus’s death.