I have an inexpensive Brother machine my 'grands' like to use. Have had it for 4 years; it is a workhorse and it sews well. It has some embroidery stitches that they like to play with, and has a slide for speeds - slow, medium and fast. It was less than $100 when i bought it, so I definitely got my money's worth.
Lately, I've been using a Janome "New Home" machine i got at Good Will for $ 12.21 (all it needed was a cleaning and oiling!) because it is much heavier and doesn't slide around on the table like the Brother does. It's very hard to sew a straight seam if your machine is slipping away from you...
I agree that the kids will outbrow a 'kid' machine very quickly.