Editorial update · Updated October 19, 2026. This page has been rewritten; historical models and events are identified in the text.
A booster’s most important work happens where the vehicle belt meets the child. The Peg Perego Viaggio Flex 120 provides several adjustments to help shape that fit, but those adjustments still need to be evaluated in the actual seating position. A comfortable display-seat trial is only the beginning.
This guide concerns the US Viaggio Flex 120. Peg Perego uses related names in other markets, where labels and requirements can differ. Match the exact model and market to the instructions before borrowing an installation tip or comparing specifications.
First decide whether the child is ready
The Flex 120 is a belt-positioning booster, without a built-in harness. The vehicle’s lap-and-shoulder belt restrains the child. Meeting the printed size minimum is one requirement; staying properly seated for the complete journey is another.
A child who repeatedly leans out to reach a sibling, slides forward or places the shoulder belt behind their back needs the problem addressed before continuing in that arrangement. If an appropriate harnessed seat still fits, it may remain the more workable option. Use the booster-readiness guide to assess the transition.
Use the adjustments to solve an observed fit issue
The US product information and Flex 120 manual describe independently adjustable head and back support, width settings and recline. Adjust the booster in the order specified, then look at the belt route with the child seated naturally.
An adjustable feature is valuable when it improves the allowed fit. Moving everything to its widest or tallest position in advance may make the seat harder to assess. Begin with the settings appropriate for the child, verify that each locks and recheck after moving the booster to another vehicle.
The armrest-free layout does not remove the need to follow the prescribed lap-belt route. Teach every adult who helps buckle the child where the belt belongs. The familiar routing on another booster may not match this one.
Rigid anchors hold the booster, not the child
The Flex 120 has rigid lower-anchor connectors. Its US manual permits use without them and recommends them where compatible. With either arrangement, the child still needs the correctly routed vehicle lap-and-shoulder belt.
Check the seating position’s anchor locations and buckle access before attaching the booster. The connectors should not force the shell into a position that compromises belt routing or vehicle compatibility. If the prescribed installation cannot be achieved, use another permitted position or another booster rather than adapting the hardware.
Also learn the unoccupied-seat instructions. Folding the backrest is a storage or transport function; it is not a riding position for a child.
Test a full buckling routine
Ask the child to sit back, buckle and settle as they would for an ordinary journey. An adult should then check the result. Look for a lap belt positioned low across the appropriate body area and a shoulder belt that follows the guide and stays properly placed as directed by the manual.
Have the child lean forward slightly and return upright while parked. The belt should resume its correct position without catching. If it hangs up, inspect the guide, headrest adjustment and vehicle belt geometry. Do not add clips or padding to manufacture a fit the booster does not provide.
Check the neighboring passenger’s space too. A booster that fits its own occupant may still block another buckle or crowd another restraint. Our high-back booster guide gives further comparison points for a shared row.
Folding is useful only if setup stays reliable
For families who move a booster between cars, a folding backrest can make carrying and storage easier. Practise reopening and locking the seat before relying on that feature during a rushed transfer. Inspect the belt guides and settings again after unfolding.
The Flex 120 deserves consideration when its adjustments produce a stable, comfortable belt fit and the daily buckling process works for the child. Compare it with the Maxi-Cosi RodiSport guide if you want to assess another booster with lower-anchor equipment. Let the fit in the vehicle decide between them.
