Diet for ADHD toddler

My daughter’s Principle told me that my toddler daughter may have mild ADHD symptoms, she suggested that we should cut her intake sugar at home first like sweet snacks and cake. She also will help me to keep take a look at school, if no improvement for one month then only go to see Dr and diagnosed.

But we have a problem at home, my whole family in laws like sweet stuffs and always let my kids eat these. Especially my FIL, when I said No, he tends to do this behind my back. My MIL on the other hand, keep on comparing on her day and now, how her kids always eat and have no issue, nowadays come out problem of hyperactive then a lot of things cannot do. I told her time has changed, last time foods or snacks don’t have chemical like now, need to see the kids situation as well.

My husband used to keep the mouth shut about this, but I told him u should speak up if u want to protect ur kid’s health. But I still feel they are not cooperating and resent me about it.

Particularly, my FIL just brought a whole roll of sweet cake home and put it in front of my kid. How do u take care ur kids diet in this situation? Will u totally eliminated sweet stuffs or still allowed them a bit everyday?