Paris prosecutor's office confirmed the arrests but gave no details of where the teenagers live, their identities, or where they were arrested.
One of the teenagers returned home after police alert but French officials fear the other 'radicalised' girl could be trying to head for Syria.
Up to 150 young French women and girls have joined groups such as Islamic State, often driven by discrimination back home.
The pair, aged 15 and 17, were arrested on suspicion of helping a 14 year-old girl travel to Syria to join jihadist forces.
Three youths detained after the mentally-disabled 18-year-old victim, who was physically unhurt in the attack, was pushed into a stream.
The pair were brought back to France having gone to Turkey in early January with the intention of joining Islamist fighters in Syria.
The bus was carrying some 50 German teenagers to Spain when it ploughed into the back of a lorry on a motorway in south-central France.