Implementing Medi-Cal coverage expansion for hundreds of thousands of undocumented immigrant children will be complicated. In addition to the many children with no prior coverage, many others currently have some form of coverage that is administered separately from Medi-Cal, such as Healthy Kids, other county programs, or the Kaiser Permanente Child Health Program. And some are enrolled in more than one program. Children with existing coverage are at risk of having their coverage, care, or both disrupted during their shift to full-scope Medi-Cal. This report explores how informed collaborative implementation of the new coverage option can help maximize the benefits children and families realize from the new coverage option and mitigate the risk of disruption in coverage and care for those already enrolled in comprehensive coverage. While the paper focuses primarily on transitioning children from the 10 county-based Healthy Kids programs to full-scope Medi-Cal managed care, it also provides information on other coverage programs for these newly eligible children, as many of the issues discussed are applicable to children transitioning from other programs as well.