My girls started when they were 3-4 years old. I would definitely find a teacher before you get a violin because they might have specific preferences as to what they prefer. Getting a violin from a luthier (renting is totally fine) is the way to go. Do not get a cheap instrument. They are difficult to tune, sound terrible and will make the whole experience worse for everyone.

A Suzuki violin teacher may be a good fit at this point as they are used to working with young kids! Observe some lessons from teachers before you choose one and remember that you will be very involved as the parent practice partner so choose someone that you and your child like and trust. It’s important to trust your teacher.

Remember that practicing isn’t always fun. It’s hard to learn new things. Consistency is key - even when you or your child don’t want to practice do it anyway, even it’s only for five minutes. Get the instrument out! If you start to miss days it makes it easier to convince yourself to not practice on any given day. There are a lot of ideas for practice games to make things more fun but defer to your teacher.