Without more information about the problem (i.e. which web page you're looking at, does it actually happen for every website you visit, etc) it could be challenging to know why this is happening but here are a couple ideas:

1. I'd say modal.js on the site you're looking at (or a site you have looked at - see below) is logging things related to children of some element to the console. If this is the case, you can clear the console log but, unless you control the site, you won't really be able to prevent it.
2. If this is showing up on every web page you visit, it may be the case that your logs aren't being cleared between different pages. You can check if this is the case by looking in your Dev tool settings to see if the "Preserve log upon navigation" setting is checked (see below for how to check this). If this option is selected, you should be able to deselect it and it may stop showing that on every page.