This study explored how early childhood intervention (ECI) professionals could support the development of secure attachment in children with developmental delay or disability (DD) within the context of ECI in Australia. Secure parent--child attachment is conducive to the aims of ECI to enhance the development, well-being, and participation of children with DD. Constructivist grounded theory methodology was applied to collect and analyze data from in-depth, semi-structured interviews with three parents and 18 professionals. Seven conceptual categories were selected: (a) Importance; (b) Challenges; (c) The System; (d) The Key Worker; (e) Assessment; (f) Strategies; and (g) Outcomes. Two dominant themes were identified: the quality of the relationship between the ECI professional and the family and self-regulation. An attachment-focused ECI framework is proposed, aligned with the ecological system model.