Simplify the following text for a Grade 6 native English-speaking person.
Original: While they are not major teratogens , uncertainty remains as to whether they cause cleft palate in a small number of babies and whether neurobehavioural effects occur as a result of prenatal exposure ; they are known to cause withdrawal symptoms in the newborn .
Simplified: They are not teratogens , but they may cause cleft palate in a small number of babies .