let up on (somebody) = be less strict with (somebody)
- I will not let up on you until your grades imrove, young man.
- You put too much pressure on Tony and he 's only twelve. Let up on him.
- Your daughter got three straight As for her school projects and just one B and you 're not satisfied with her work? Let up on the girl!
- My wife says I 'm too strict with our kids. Maybe I should really let up on them a bit.
- No, I will not let up on him! He promised he would wash the car and he didn 't. That is not very responsible of him.