How to ask husband and MIL not to start Cerelac etc till 6months old

Hiya,

Husband and his family can’t wait till baby is 4 months so they can take baby and spend time with her and give her cerelac whenever she cries for food. However, I’ve read it’s advised not to start solids till after 6 months old, as the digestive system is still premature before then.

How do I inform them kindly and with love of this? I’ve even asked the GP with my husband present, who stated 6 months for solids, but he’s sort of dismissed that (as he’s from a country where they start solids at 4.5months), and if I speak out against his family, it’s to my detriment.