I think if a parent wnts to do things for their children, that's their choice. I didn't ask my folks for much, maybe babysitting when the kids were small. But if they offered? You bet your ass I'm accepting.
20+ years ago, my twins were in preschool and I was drving a 1993 Pathfinder. It was paid off and ran fine, not that it mattered because we couldn't afford anything else. It fit the double stroller and all the other shit. My mom felt differently. "I don't like you driving the kids around in that old car.", she said one day. I told her that's too bad because it's what I can afford. She said she'd trade me her 2001 Mazda SUV for my car and she'd trade it in for something new for herself. Done and done, you bet I jumped on that deal.
"We want to buy XYZ for the kids", go for it. "Here's our old [hosehold appliance], we're getting a new one", I'll take it. When I moved into my house 13 years ago, my dad decided to buy us a washer and dryer. He had gobs of money and won't miss it, I said knock yourself out. But I never would've asked him for a dime.