When can you start using a gro-bag?

[Gangle]

DS is 5 weeks old and really keen to start using a gro bag as often paranoid that he is too hot/too cold but I remember reading somewhere that they weren't recommended for babies below a certain age. Anyone know what age they can be used from? Also, do they make middle of the night changes more difficult and what should DS wear if using one?

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I read the title and thought we were talking tomatoes...opps

From Grobag website:

An ideal time to start using a grobag® baby sleeping bag is when your baby weighs more than 7 lbs (0-6 mths size). It is very important to check that your baby?s head cannot pass through the neck-hole when the grobag® baby sleeping bag is fastened for use. Please remember that these are recommendations only as all babies are different. Make sure that your baby?s legs and feet have freedom to move about, by ensuring that the grobag® baby sleeping bag is long enough for your baby. The lengths of grobag® baby sleeping bags (from shoulder to bottom) are:
0-6 mths 76cm,
6-18 mths 94cm
18-36 mths 112cm
3-6 yrs 128cm