If the bowls are plastic bowls I always them in the top rack so that they are not near the heating element in the dishwasher.
If you place the plastic bowls or even plastic cups on the bottom rack they can get thrown around and get melted by the dishwasher heating element.
So always put any plastic bowls or cups in the top rack of the dishwasher to avoid them melting.
If you want to put glass bowls or glass cups including ceramic mugs on the bottom rack you can do so.
But I always just put all bowls including glass bowls, glasses and ceramic mugs on the top rack and put plates that are ceramic on the bottom rack.
The top rack has less room so smaller dishes should go on the top rack and larger dishes such as ceramic plates and large bowls should go on the bottom rack of the dishwasher.