If you are an adult you many not want to be "slowed down" with children in your class and conversely, you may not want your child training with adults.
This is not a right or wrong answer but a matter preference. If the focus is on tournament participation, much of the time and effort will be spent in preparation. If this doesn't interest you than perhaps you should choose another instructor.
A contract isn't a bad thing but be clear that you understand the cost, the length of the commitment and the circumstances (if any) under which you can terminate the contract.