DH has been making porridge for us both each morning for breakfast, tried it out on 10month old DS who loved it, prob cos it makes a nice change from fruit and yoghurt! I know you're supposed to give babies full fat milk,will it matter if we make the family porridge with semi-skimmed? Just seems a waste of full fat that won't get fully used just for DS's morning porridge!
Semi-skimmed isn't harmful, it's just that full-fat has more calories which is important for babies' growth.
So I would say it depends how much porridge he has and if it's every day. I would say if it's a big enough portion that it's his only thing for breakfast and it's his breakfast every day, it would be better to use full-fat. You would probably use one pint by the time it went off, or you could decant half the pint carton into a bottle/empty milk carton/other container and freeze it.
I tend to make DS' porridge by heating the milk in the microwave, but then I am using ready brek as I bought 2 boxes when I was pg (was on offer) and then decided I didn't like it This is only relevant if you need to make his separately because you don't want full cream milk in yours (I also prefer full cream milk in coffee, another good way to use it up)