Strategies for getting involved in students' work during labs? As a TA I conduct computer laboratory classes (the lecture is conducted by one of the professors). These are part-time studies, so labs take place during weekends, 3 clock hours each. Some students are older than me and are mostly male (I'm female). Some students have longer job experience than me, but I still feel I can teach them something important, not particular technologies, but rather an engineer attitude.

I prepared detailed written tutorials for these classes, which students follow step by step. At particular steps there are some general remarks included, like as you just saw, it's a good idea to include validation both at client and at the server site. The reason I don't say these remarks by myself, is that the speed of work differs significantly from student to student.

The result is that I don't have anything to do during these tutorials. I say a small introduction at the beginning, but it's not extensive, because the theory is covered at the lectures. Students don't ask me for help because the written tutorials address a large set of mistakes that students from previous years already did. When they really don't know what to do, they ask their colleagues.

In rare occasion they ask me a question I rush to them and explain everything, I also say in the beginning that if they have any questions I will be happy to help, so I don't think I deter then from asking for help.

But still I sit silent for most of the time. I only make few rounds around the lab, asking if they achieved the particular step, but they say they did and that's all. The rest of the time I do other things related to the classes (for example review tutorials, check homework, answer emails).

Last year I overheard students saying they like the written tutorials very much, because they are clear and include everything they need. Still I'm worried they can give me bad notes for my teaching, because from their perspective I do nothing and I am of no use to them during labs (last year my final score wasn't count because too few students decided to grade me).

What could be strategies to make tutorial-based lessons with tutorials more interactive? Or maybe I should not worry about it?

My idea was to make the tutorials more vague so that they ask more questions but it seems ridiculous. The tutorials are also used by students who could not attend classes or couldn't finish during labs. Also only first part is step-by-step, because the second part contains homework, on which they can practice self-reliance.

Edit

This situation also makes them ask if they can do the work at home, without attending labs and just send in homework. I'm ok with that, but I think my department is not.

I also had a situation when student send me an email with finished task during labs instead of showing it to me.
From your post it appears that the labs are already highly interactive. Students are engaged working on the assignment among each other. From an education perspective the current learning environment is student-centered, which is often the ideal.

However, one common drawback to an engaging, student centered environment is that the teacher is not the focus of the learning. This can be somewhat un-stimulating for the teacher but the goal is always for the students to have maximum involvement. 

One option for dealing with this situation is to shift from trying to lead the students to provide expertise when necessary. When students have questions be available to answering them. Another useful strategy is monitoring. This involves observing student progress and providing additional unsolicited support.