Sewing machine that does NOT stitch!

To whom it may concern,

In December 2017, I bought my two daughters the Toys R Us sewing machines as Xmas gifts. When they finally opened the sewing machines, the machine stitched but the stitching does NOT 'stay'. In other words, when you sew, the stitching does not remain and therefore they are unable to stitch pieces of cloth together - which defeats the purpose of the sewing machine actually.

Please can you assist me a.s.a.p.

Thanks in advance, Heidi