(one) could be (someone's) (parent/grandparent)

One is old enough to be someone else's parent or grandparent. Used in reference to two people who are or may become romantic or sexual partners, especially to indicate that the speaker thinks such a pairing would be inappropriate. He's going out with Mary from the legal department? But she could be his mother! I don't feel comfortable with this. I could be your grandfather, for heaven's sake! I highly doubt Ron and Elise are going out. For one thing, he could be her father. For another, they're always squabbling with each other.

(one) is old enough to be (someone's) (parent/grandparent)

One is old enough to be someone else's parent or grandparent. Used in reference to two people who are or may become romantic or sexual partners, especially to indicate that the speaker thinks such a pairing would be inappropriate. He's going out with Mary from the legal department? But she's old enough to be his mother! I don't feel comfortable with this. I'm old enough to be your grandfather, for heaven's sake! I highly doubt Ron and Elise are going out. For one thing, he's old enough to be her father. For another, they're always squabbling with each other.

co-parent

Of a set of parents who were previously married or in a relationship with each other, to jointly raise their child(ren). My ex-boyfriend and I co-parent, so the kids will be with him this weekend. John co-parents with his ex-wife. I wish I could cut my cheating ex-husband out of my life entirely, but I can't because we have to co-parent our two kids.

helicopter parent

A parent who is overly attentive and doting toward their child or children. The term comes from the notion that they are "hovering" around their children at all times. Don't be a helicopter parent. Your daughter is 18 and fully capable of picking her own classes. I don't want to be a helicopter parent, but we live in a dangerous world, and our kids need protection! He can't make a decision on his own because his mother's been a helicopter parent his whole life!

stay-at-home parent

A parent who forgoes employment outside of the home in order to care for their children and the household. Being a stay-at-home parent is just as much hard work as going to an office every day. The government has announced a series of financial supports for new stay-at-home parents choosing to leave the workforce.

step-parent

A caregiver of a child who assumed the parental role through marriage to one of the child's original (usually biological) parents. Most commonly, a step-parent is the second spouse of one of the child's biological parents. Through my marriage to Kent, I became a step-parent to his three beautiful daughters.

tiger parent

A particularly strict parent who makes their child or children work very hard in school in order to achieve success. Said especially of parents of Asian descent. I had always told myself I would not turn into a tiger parent like my dad before me, determined to let my daughter enjoy a more carefree childhood than I was afforded. My friends and I always joke about how the only reason we got jobs was because our tiger parents made sure we never took a day off from our studies.