baby sit-up chair / baby sit trainer / seat trainer

They feature a wrapping 360-degree padded support frame, front leg leg openings to keep infants secure from tipping, and a soft fiberfill interior wrapped in hypoallergenic velvet or fleece.
"Sit Me Up" floor trainers or baby support pillows. These lightweight plush chairs are ergonomically engineered to assist infants from roughly 3 to 24 months old as they build core stability and learn to sit upright independently