Should i use glass inomer for filling teeth for child in 3 years old?

Excellent question: And yes is my answer. Also consider compomers (like dyract). Strength of material issues come into play with large load bearing restorations, so "keep em small" or consider different materials. With caries in a three year old the glass ion is an excellent choice and the causes of decay need to be addressed. Hope this helps!

Priorities: Dr. Hinson gave you a great answer. For fillings in 3 year olds, my priorities would be to do the best filling possible while making the experience as pleasant as possible for the child. Whatever works best in your hands would be fine.