I used to have zebra finches they only eat seeds really.
Can zebra finch eat crackers?
As they mostly eat seeds, I don't think crackers would be to good for them. Here's a list of foods for them.
What Human Foods Can Finches Eat That Are Healthy for Them .
I don't know about zebra finches but I have a parrot who likes a little bit of a cracker but you have to make sure there is no salt at all on there, birds can't handle salt.
I'd stick to other bird treats.