It is definitely worth investing in an air purifier. I have two year old twins who were always falling ill in Delhi. The kids perpetually were on a nebuliser and if one fell sick the other one automatically fell sick.
I have now got a purifier in their bedroom which is constantly running and they don’t fall sick as much and definitely don’t pass anything on to each other or us.
I have tried 4 different companies, Sharp, Daikin, Panasonic and Airoshine.
I would recommend you have a look at the Airoshine air purifiers. they have 8 filters and a PM 2.5 counter on the front that lets us know exactly the air quality and condition in the house. I think they are the best in the market for indian conditions. Their website is https://airoshine.com if you want more information or want to order one.