Hie.. at first, get those cavities restored/filled before it leads to some painful events for the child in the future.. since she is just 3 years.. her first tooth come at arnd age 6-7 years.. so better to get them restored .. next, if she is not being able to brush every time atleast rinse her mouth with plain water..

Get check up done by a Pedodontist. Brush her teeth after every meal , even after she has milk . Avoid overnight bottle feed.Cavities should be treated.

"How to Protect Milk Teeth (Child Teeth)?" by Dr.Rashmi Bamane - https://www.practo.com/healthfeed/how-to-protect-milk-teeth-child-teeth-39707/post

Hi. Noticeable cavities has to be filled. Visit a pediatric dentist at the earliest before the cavity extend further and get it restored(filled) Post that every 6 months follow up check up is must. (Rule out if any habit like pouching of food, pooling of milk in mouth is there.)

Hie .ya avoid sticky food , brush her teeth twicely , after consuming milk get her mouth to be cleaned with water, avoid night bottle feed