Two factors need to be kept in mind to understand the loss of Jesus. At age 12, Jesus would have been considered almost an adult in that culture at that time. Perhaps it would be like a 17‐year‐old in our culture. It does not pertain to parents to keep as close a watch on a much older child as with a very young child. 
 
Secondly, pilgrims making the journey from Galilee to Jerusalem and back, a walk of over 70 miles, often walked in fairly large groups. It was common for people to divide out, women walking with women, men with men. Older children might also walk together; the younger children would stay with their mothers. 
 
As an older child reaching adulthood it is easy to understand how Jesus might have walked with a group apart from his parents. And this would go unnoticed until the evening when families would reunite. Immediately upon noticing Jesus' absence and inquiring among other relatives, they rushed back to Jerusalem to find him. 
 
With these two factors in mind, they were not negligent. The temporary separation from him was understandable, and immediately upon noticing it they saw him out. 
 
As for Jesus’ reaction, it is mysterious. But we need to remember that we cannot hear his tone of voice. Further it could simply be that he was surprised in terms of his human knowledge at their wonderment in a genuine way, figuring they knew where he was.

It varies according to each. Priests are not “paid” for celebrating funerals. And while it is customary for many families to give the priest a donation or stipend, Church Law does not require such a donation. Such donations are generally small or tokenary since priests are well cared for by the parish already. And while priests can and do accept such donations, any notion that what they receive is a “fee” is to be avoided. Priests must be willing to celebrate liturgies and sacraments even when no stipend is offered. This is especially the case when working with and caring for the poor. 
 
Organists and Church musicians are another story. They can and should be paid. They have spent years in preparation and practice, and the monies they receive are usually part of their livelihood. Often, they must leave other obligations to cover funerals and may have travel expenses. If families wish to engage their services, musicians and organists should be compensated. In cases where there is poverty and a family cannot afford to cover even basic music, the parish can help. But since elaborate music is not required for funerals, the requested help should be reasonable. 
 
As for servers and sacristans, the practice of donations is less common. In some places it is customary to give the servers a small donation; in other places not. Sacristans are seldom given donations. Servers and sacristans are generally presumed to be volunteers, and while a young server may appreciate a $20 dollar bill, it is generally not expected. This is even more the case with adult servers who would likely be embarrassed by receiving a donation.