1.-"I never do songs with my group of 10-year-olds. They think singing songs is for babies."
Even though I concur that using songs might be a easier way for children to recall certain aspects of a language, certainly using songs for 10 year old children might no be the best option; due to the fact that they starting a either physicall and cognitivite changing process where they don't feel anymore as children but as grown ups and they want to stop doing infantile activities. Therefore as a teachers we should be more flexible on that aspect and only use song when appropiate.
2.-"I always start the lesson with a review of the previous lesson. And I always end the lesson with a song."
Without a shadow of doubt this should be how a lesson ought to start. Most of the times, after school, unfortunately, children go home and they do not have the opportunity to review what they have done in class during that day. Having a review from the previous lesson at the beginning of a new lesson to ensure that students can recall, for instance, vocabulary from a prior lesson and start a new class to introduce more language hence is what all teacher ought to do.
On the other hand, let me consider that the lesson had an important amount of new language introduced; thus, ending a lesson with a song is the best choice. Teacher can take advantage of a familiar song to students that include what they practiced during the class and they, the students, can enjoy and relax by the end of the class.
3.-"I prepare extra exercises for the children who finish early. It's not good if they have nothing to do."
This option can clearly be seen as the optimal one, no a single a teacher wants a child who is finished with a task or activity and starts distracting the rest of the group and I think as an observation the activity might not be one who distract the others as well. Although it is also possible to consider to assign the children who finished first the "tutor" role, meaning, they are going to help their classmates if they have difficulties on understanding the activity or work in class; however, this might work better only for the young learners that are older.