If parents let their kids have a smartphone, it makes life easier for the parents.
ーIf parents let their kids have a smartphone, they get glued to their phones for long periods at a time which makes life easier for the parents.
「親が子供にスマホを持たせると、子供はスマホに夢中になり、親にとっては楽になる」
If parents let their kids have a smartphone, it makes life easier for the parents. で「子どもにスマホを与えておけば、親はラクできる」と表現できます。
to get glued to ... で「…に夢中になる・釘付けになる」
ご参考まで!