Roedd Bil Plant a Theuluoedd y Deyrnas Unedig hefyd yn cynnig cyfleoedd i newid trefniadau trawsffiniol rhwng Cymru a Lloegr: mewn perthynas â datgymhwyso Cofrestr y Ddeddf Mabwysiadu a Phlant yng Nghymru; darparu triniaeth gyfartal i unigolion a fabwysiadwyd a'u perthnasau, i bennu'r terfyn amser ar gyfer paratoi cynllun gofal i blentyn. Gwnaed y trefniadau olaf hyn drwy roi pwerau gwneud rheoliadau i Weinidogion Cymru mewn perthynas â gosod terfyn amser i awdurdod lleol orfod paratoi cynllun gofal wedi iddo wneud cais i'r llys am orchymyn gofal neu oruchwyliaeth. Mae a wnelo diwygiadau pellach sy'n ymestyn i Gymru a Lloegr ag anghenion addysgol arbennig, rhannu cyfnodau absenoldeb rhieni a gweithio hyblyg, gofal plant a'r swyddogaeth gryfach i'r Comisiynydd Plant.
The UK Children and Families Bill also afforded opportunities to change cross border arrangements between England and Wales: in respect of the dis-application of the Adoption and Children Act Register to Wales; providing parity for adopted persons and their relatives, to prescribe the time limit for the preparation of a child care plan. The latter arrangements have been made by conferring regulation-making powers on the Welsh Ministers in relation to setting a time limit by which a local authority must prepare a care plan following its application to the court for a care or supervision order. Further amendments that extend to England and Wales are in relation to special educational needs, shared parental leave and flexible working, childcare and the stronger role for the Children’s Commissioner.