Talk to the dwarf in one of the huts in the Dwarf Village. He will mention his lost son and ask Tomba to help him find his son.
Go to the right part of Watch Tower, where a L-shaped pink platform can be found. Make a running leap to the left to find a platform. Continue to the left and avoid/defeat the Spider. After that, you'll find a little kid walking back and forward.
Talk to the kid, and he'll say that he was looking for Flower Seeds and wants to go home. Talk to him again and he'll jump onto Tomba's back. Now you want to go back to the Dwarf Village, where the son and his father reunite. The father will reward Tomba with a Cheese. The event is cleared.