"dar uno"?

[createdamadman]

In the sentences below, I understand that the manager is basically giving the kids a tour, but I don't understand why "dar uno" is used.

[Rusty]

I would expect a second personal 'a' in the second sentence: a María y a Roberto.

I believe you might be thinking that «dar uno» is short for «dar un paseo», but what follows ('in construction work') doesn't make any sense.
It makes more sense if «en la obra en construcción» is translated 'at the construction site'.

Depending on where you live, «dar un paseo» typically lasts longer than a tour of a construction site. I would say we're talking about «un recorrido» here.

Let's see what a native speaker has to say.

[AngelicaDeAlquezar]

I agree with Rusty.
The second "a" necessary in formal writing, but in daily speech many people suppress it. ;(

And I agree that without any context, "uno" doesn't make any sense. Here, "uno" is a pronoun that most probably substitutes "un recorrido" or "un paseo" mentioned in a previous paragraph.

The pronou, by the way, must agree in gender with the thing it substitutes.
- Le regalé a mi mamá un sillón reclinable, pero también quiero uno para mí.
I bought my mother a recliner, but I also want one for me.
- Tengo que ir a la farmacia. Creo que hay una de camino al trabajo.
I have to go to the drugstore. I think there is one on the way to work.
- Compré dos donas. Te puedo dar una.
I bought two donuts. I can give you one.
- Hay chocolates en la mesa. Dale uno a cada niño.
There chocolates on the table. Give one to each kid.
- Mira estos adornos navideños. ¿Hacemos unos para decorar la casa?
Look at these Christmas decorations. Shall we make some to decorate the house?
- Yo tenía unos audífonos con cable retráctil. ¿Sabes dónde puedo encontrar unos así?
I used to have some earphones with retractable cord. Do you know where I can find some like those?
- Corté unas flores del jardín. Puse unas en el comedor y otras en mi recámara.
I cut some flowers from the garden. I put some in the dining room and some others in my bedroom.
- Esas botas están muy bonitas. Me gustaría tener unas.
Those boots are really pretty. I'd like to have a pair.