Usually had parents asked:How old children start to learn the violin is good? Normally 5 years old is good, but it is not absolutely,every children is different,consider the following points:
If your child has a good rhythm,try to follow music or youself singing and clap your hands to start practice.
If your child like singing very much, have good intonation,then he already had advantages to learn stringed instruments.
If your child already had this two conditions,also he has a healthy body especially strong hand muscles then can be sure,he can learn the violin now .
If your child has all of these qualities,also like the violin very much,you can choose a teacher who is professional and had experiences,patient and loving to teach your child learning the violin and enjoy nice music.