Over many years as a music educator two of the skills that young musicians have trouble developing are steady inner pulse and counting. Here is a simple technique to improve both at the same time.
Step 1 Have the students count to a metronome out loud to get everyone to actually count.
Step 2 Have the students start counting silently and then cue them on random counts to speak the number they are on at that given moment. It will take a few times of starting/stopping to get everyone to speak the same number when cued.
Step 3 Once the class is really concentrating on counting correctly I then start them with a metronome and then turn it off so that the students must collectively use their inner pulse to silently count as an ensemble and speak the correct number when cued.
The students tend to really enjoy this process because it feels like a game.

I hope that this is helpful for you and your students and it helps everyone to have a successful music experience!