I am picking up a friend and her two children tomorrow for a playdate. She has a 10 month old and a 2 yr 9 months old. Yeah I know I broke it down weird I am on mobile bfing a baby and it's midnight. The two year old is massive for her age. Height weight she is just BIG it's genetic her father is linebacker big. She is in a booster seat. is this safe? It's a backless booster.