Not everyone has received the news about sugar and considering that just about every comfort food we have is loaded with it, it’s going to be a while before the low-sugar story becomes mainstream, I’m afraid.
Nevertheless I think you should have a quiet word with the childcare, and perhaps send him with his own food. Jam sandwiches to a 10 month old indeed! It isn’t going to poison him or anything but the (relatively new) principle of avoiding foods with added sugar to anyone under one year (or older, for that matter) still stands.
We’re all primates and love sweet things, or any other energy dense food, because we evolved when such foods we’re rare in nature, and we grabbed them when we could, as famine was not unusual. Sweet things are sweet to taste because they are loaded with fructose, and we now know that half of the energy from fructose goes straight into our fat stores. If it is in the form of raw fruit it is better as the fibre reduces the volume and mode of absorption. Because of its rarity during evolution we did not need to develop an ‘off’ switch to our appetite for fructose, and hence it is somewhat addictive. So, given the chance, we tend to eat too much of it.
So it has the tendency to make you fat (unlike fat in the diet that actually curbs your appetite).
Under one year olds are still in the process of learning what is good to eat, and they learn it been experience and by copying what the adults around them seem to be enjoying.
‘Children eat what they like, and like what they know’
After one year they develop increasing ‘Food Neophobia’, that is fear of new tastes. That is a evolutionary. When you get mobile it is a good idea that you become resistant to eating unfamiliar foods, in case you go into the back garden and poison yourself on some berries you find.
So it’s a good idea until they are over one year to avoid all the foods that you do not wish them to accept later, and to give them only healthy, wholesome food.
A single instance of a jam sandwich is not going to teach him too much, but it shouldn’t be repeated if possible. You and the childcare should all sit down and see the following lecture about sugar by Dr Robert Lustig, Paediatric Endocrinologist from San Francisco on YouTube.
Ref: Lustig R.H. “Sugar: The Bitter Truth” UCSF, Mini Medical School, YouTube 30th July 2009