from jetstar's website (Travel info - Family travel -What to take)

Strollers and Pushers
We understand how indispensable compact strollers or pushers can be on holiday. Most parents with small children wouldn?t dream of going away without one. Nor should they have to. At Jetstar we?re happy for you to bring one along in addition to your regular baggage allowance.

On domestic and Tasman flights you must check pushers or strollers in with your other luggage. Larger pushers can travel as ?special luggage?. Make sure it clips shut so it?s easier to handle.

For your convenience parents can bring a fully collapsible pusher on-board our A330s (International long haul flights) so long as it is no bigger than 100x25x23cm.

HOT TIP
While we always do our best to ensure your luggage arrives safely, sometimes strollers can be damaged in transit. Protect your stroller by placing it in a bag or in plastic wrap.

ETA:
Bulky Items
All the extra gear can make travelling with kids feel more like you’re moving house than going on a holiday. Strollers, car seats, toys, bottles, nappies, kitchen sink. Whether it’s for the weekend or a month, there are things you just need. At Jetstar we’re happy for families to take these essential items, especially things that are going to make the holiday more comfortable and safer. Here’s a list of the bulkier things families can check on Jetstar flights without attracting excess baggage charges:

Strollers or pushers
Porta-cots and bedding
Infant car seats
Portable high-chairs

Anyone who has paid for a seat is entitled to the full baggage allocation: 20kg of check-in and 10kg hand luggage. Another great reason for purchasing a ticket for infants.