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Direct and Indirect Objects

it seems to me both are correct.

letz see what the native have to say on this ;

In Arabic there are intransitive verbs (verbs that can't have a direct object) like جلس he sat down
ex: جلس أحمد Ahmad Sat down (No object)

and verbs that are transitive with one object like درس he studied.
ex: درس أحمد اللغة العربية Ahmad studied Arabic language

and verbs that are transitive with two objects like أعطي he gave
ex: أعطي المعلم مها كتابا the teacher gave Maha a book. where مها is the first object and كتابا is the second object.

So the right one is to say
أعطوا مها كتابا جديدا (Notice the tanween with fat-ha for the object and its adjective)

The other form although it's understood but is less eloquent since there isn't really a need for the preposition "ل" .So you can say :
أعطوا كتابا جديدا لمها they gave a new book to Maha
or
أعطوا لمها كتابا جديدا They gave to Maha a new book
and it's understood.

but I think it's an incorrect use of أعطي so better use a direct object when the verb takes 2 objects

Other examples for transitive verbs that take 2 objects :
منح - وهب both mean "he granted"
وجد he found. for example : وجد أحمد الطريق طويلا Ahmad found the road (to be) long
اعتبر he considered : اعتبر أحمد كلامي مزاحا Ahmad considered my words (to be) a joke