I wish but.....
Umpires & refs would be lovely but would add to the cost of your tournament entry.
So teach your child to call the score loudly at each point, whether winning or losing, when serving.
If there is a discrepancy it can be sorted there & then. The kids aren't arguing about a call 3,4 points ago.
If their opponent doesn't call the score, get your kid too and make sure that they use the score boards.
If it is cheating/ hooking there are loads of threads on what to do.