Yes, all the solder included in CircuitMess kits is lead-free (RoHS compliant).
Even though it's lead-free, we still recommend soldering in a well-ventilated room and wearing the Protective Goggles included in the Tools Pack. Proper ventilation keeps solder fumes to a minimum.
If you're new to soldering, the build guides on our Resources blog at circuitmess.com/blogs/resources walk you through the technique step by step.