How do you increase vocabulary?

I agree with Adam. Some children (like your daughter) are motivated by the flashcards on their own. Others need more creative thinking and often an active element. I've played the flyswatter game a lot with children and it works really well. Usually the more active and crazy the better.

However, I think that for some children they respond even better to objects. The sensory experience seems to promote better learning. You can gather household objects or use toys eg toy animals, objects from a dolls house or even use large objects around the house. If your son is needing extra motivation you could make it a game where you play against him and the au pair directs it eg first person to find x or touch y. Or simply pull each object out and the first person to name it gets to keep it and the winner has the most objects at the end. Another way to build vocabulary is the au pair saying eg find me something red/ made of wood/ fluffy/ thin etc so describing the object instead of just naming it. If you don't have time to play they could play against a timer. All of these activities can also be used with flashcard pictures.

For this type of activity if your son isn't showing much interest it might be that he needs to find it easy and experience success to be motivated to play. Try playing a game where he knows all the words and once he is finding the game enjoyable introduce one or two new words at a time, waiting until he has mastered them before more are introduced. Some children feel overwhelmed by too much new knowledge at a time while others view it as an exciting challenge.

The main way preschools and schools teach children new vocabulary is through studying topics. Eg houses and homes, read books about them (fiction and non-fiction, walk around the neighbourhood and take photos of them, draw/paint/make collage pictures of different types, build different homes with eg lego, junk modelling, clay, making a den, find out about unusual types of homes using the internet eg igloos, homes on stilts, houseboats, learn about different animal homes, learn a song with a house theme, play with model houses. The topic can be anything eg farms, zoo, north pole explorers, fire safety, cooking, toy shops, fast vehicles, outer space, castles, plants. It works best if you take a topic a child is interested in already or start with eg a book/visit/cartoon and then discuss it and follow up on the child's interests. If you google topic planners or look on preschool websites you often see ideas for this kind of thing. A visit to a museum or library can also help to spark ideas. The repeated conversations using different activities gives lots of practise of vocabulary in context. Flashcards can be used as part of the topic study but because children learn in a deeper way about the topic they are likely to remember it better. If it is a topic they are especially interested in they often learn really advanced vocabulary that some monolingual adults wouldn't know eg some young children can name many obscure dinosaurs. I think this is a really valuable way to increase vocabulary as it doesn't just focus on a list of eg 20 nouns but will provoke a lot of discussion using questions and answers, descriptions and more complex language use.

Maybe your au pair could do a couple of topic studies with your son or both your children while she is staying. Also if she has any special interests it is often a good place to start. The enthusiasm of the adult can help a lot so if she is passionate about eg dogs, skiing, gardening, mountains it might be worth sharing that passion at an appropriate level for your children.

Adam Beck and Alison thank you so much for these great ideas! I will order some fly swatters from amazon right now! I think my children would LOVE this game. I actually remember reading about it before, but never actually tried it. But I think it will be useful.

Alison, that is some really great advice. I will try to make a topic plan, as you suggested. It's actually a fun thing for me to do. I have LOADS of books to help with this as well and can find YouTube videos, toys etc for the different topics. I kind of did this prior to the kids going skiing. I bought several different books about skiing in French - T'choupi fait du ski, petit ours brun ski, la station de ski, Les coquinettes en classe de beige, La montagne, peppa ski. I have a bit of a book obsession! I also did this for when they started school, went to dentist for the first time, the doctors and so on. I started doing this in English first and then moved on to French. However, I think I can add more to the plan as you suggested, with objects in the house, arts and crafts etc. In fact, I think I'll just copy and paste what you wrote and send to the au pair so she can read and get some ideas as well.

Will try these great ideas and report back in a few weeks.

Thanks again!

Yes what great ideas! I'm not naturally enthused by the idea of flash cards, because they seem so artificial, but the fly-swatter game seems like a lot of fun. I will also have a think about topics...

My daughter keeps randomly asking me what a word means (for instance when we're walking together, on the street), and every time it takes me a while to work out what she's saying. As soon as I manage to link it back to a book we have read together, I understand what she's asking and I can see that she's really been listening to the books. So having a context for the word definitely seems to help in her case.