I'm very recently appointed as the teacher for one of the classes in my dojo (a mere shodan) . and some of the new students told me that they're not very sure that Aikido really works without too much strength.. what would you do if you were told that?

I'm sure that my Aikido works (thanks to Sensei for teaching me well) so I was thinking of letting them attack me seriously, but I'm also afraid that they'll get hurt and it will become a big trouble for me.