Amid growing concerns about the spread of measles and other preventable illnesses, Colorado lawmakers are bringing back a bill that seeks to make it harder for families to exempt children from vaccines required by public schools. And Democratic Gov. Jared Polis — who played a key role in killing last year’s bill — says he will support it. The Senate bill, unveiled Monday, would require parents seeking an exemption for nonmedical reasons to first speak with an immunizing provider and then have the provider sign an exemption form to submit to the school, or take an online class about vaccinations, print the confirmation and submit it to the school with their exemption form.