you can take it in your hold baggage or your hand baggage as far as i know, i have done both in the past no problem, check with your airline

In the past we've taken enough for first few days and then bought out there and never had a problem.

On the subject of babies. My daughter will be 13 months when we go abroad, going to Majorca.

I don't know wether to keep her on formula milk unti we get back, or ween her of hte formula and use cows milk abroad.

What do you think I should do?

Re jars of baby food what about the small tins?
When you've finished just throw away and no chance of smashed glass in your bag!

The cows milk abroard normally has a different taste which you either like or dislike.
You could try try her with cows milk for some feeds so you don't need to take too much powdered with you.
Both my kids when babies(and now) loved foreign milk!
My daughter had breast and formular and cows milk at 13 months, just depended where we were and what we were doing.
The cartons of ready made are a god send too for travelling.

I took my granddaughter away with us a few weeks ago. We took tinned food, enough for a week and formula milk. It certainly took up some room in the cases. But once she had ate it we had room for the shopping

I would wait until you get home before changing to cows milk. Apart from the fact the formula is easier, if she/he doesn't like the cows milk or it doesn't like her/him, you could end up with a stressful holiday.