My 2.5 year old has slightly bucked teeth from thumbsucking. does this mean her adult teeth will be bucked?

No: If thumb sucking is stopped before permanent teeth start to erupt it will not have major effect.

Depends: If the habit stops before age 5 then it is less likely. If he has sucked very hard then he may have deformed his palate and may need some expansion to correct it. Most of the time if it is mild it will not affect the perm teeth. Take him to see a dentist for further consultation.

Not necessarily: There's enough elasticity in growing children that slightly displaced teeth respond well to discontinuing thumb or finger habit by age 4. If continued beyond then , can cause permanent deformation that requires more complex treatment. Has to do with both intensity and duration. If you're concerned, see a pediatric dentist or an orthodontist for an opinion. It's never too early to learn.