The Tax Cuts and Jobs Act of 2017 repealed the shared responsibility payment, which is a penalty for not having minimum essential health coverage (and not being exempt from this requirement). But the repeal doesn’t impact 2018; it only provides relief after 2018.
The tax on the investment income in excess of $1,700 (may change after 2007) of a child under age 18, based on the parents’ marginal tax rate and computed on Form 8615.