If your treats are undermining the parents’ wishes eg sweets, then it is time to change tack.
For example, I rarely give treats, but at Easter it was a £1 egg and tickets for a day at the climbing centre, which met with approval all round.
This summer I have sewn lots of name tapes on new school uniforms. That is my contribution, cost me nothing but saved their mum lots of time and hopefully keeps them from losing kit at school.
When they come to my house I offer something from the treats box but they never take more than one. Well brought up, healthy grandchildren.
The other lot of GC have always been over- indulged, and I never get a thank you for anything I give them, which seems paltry in comparison with what they have already got. So I might not bother any more.
Every family is different.