when my graddaughters started sewing at 4 years old i went with an inexpensive brother machine from wally world ($79)
the reason for this decision was because i felt it important to have (speed control) and the brothers do- it's like a governor on a go-kart- they can put the pedal to the metal- but the machine can not speed away on them.
that first brother was quite a few years ago now- and still works great.