Generally, in order to claim a dependent child on your tax return, the child is required to have spent over half of the year in your household. If this is not the case, then the child’s dependency claim lies with the person responsible for the child’s full-time housing, which in many cases is the legal guardian of the child.
Sometimes, you are able to claim a child as a dependent if they don’t live with you, provided the parent with legal custody signs a Form 8332, Release of Claim to Exemption. The same information can also be provided on a separate form, if access to a Form 8332 isn’t readily available. By signing this form, the custodial parent gives up their right to claim the dependency exemption for the child listed on the form.
Generally, this is the only exemption to the child dependent rule, as typically they are required to live with you and each dependent can only be claimed once.