Wa'alaikum assalam! Yes, boleh je ambil flu vaccine untuk anak 2.5 tahun, a few of my mum friends dah buat, and mostly okay je side effects-nya, just slight fever or moody for a day or two, nothing serious. My boy pun kena mild rashes for a few hours after, but the paediatrician said it's normal and nothing to worry about. Honestly, ramai paediatrician recommend it especially kalau anak exposed to many kids like daycare or activities, so it's worth asking your doctor whether it's the right time for your little one and whether she needs one dose or two!