Family Sharing Glitch

It is possible you activated Screen Time, or if you just recently became an adult, a parent had activated this.

Use Screen Time on your iPhone, iPad, or iPod touch - Apple Support

Use parental controls on your child's iPhone, iPad, and iPod touch - Apple Support

What restrictions are you facing? Sharing iCloud storage should not introduce any new restrictions unless the entire family has reached the limit. You say these are child restrictions but what indication is there of that? Is the age on your account set to 13 or higher (typical adult for most countries)? If it is set to 12 or lower then it is a child account and has to be part of Family Sharing.

Use Family Sharing to provide parental consent for your child's existing Apple ID - Apple Support - "Apple allows children to have Apple IDs and to use Apple services with parental consent. The age where parental consent is required depends on the country or region, and sometimes these laws change. If you have a child who already has an Apple ID but their account doesn't have your consent, use Family Sharing to add their Apple ID to your family group and give consent."