A lower leg rest device includes an engaging member and a support member having a length adjusting mechanism. An end of the support member is pivotally connected to the frame of the baby carriage at a pivot point. The engaging member is disposed on another end of the support member. The support member is used for supporting a child safety seat. The length adjusting mechanism is used for adjusting a length between the engaging member and the pivot point. When the lower leg rest device pivots to a position below the frame body, the length of the support member can be shortened so as to support legs of a baby seated in the baby carriage. When the lower leg rest device pivots to a position above the frame body, the support member can be lengthened so that the engaging member can be engaged with and support the child safety seat.