Family of six & train travel - some advice please!

Hello there. Our family of six (2 adults and children aged 12, 10, 10 & 7) are visiting Switzerland in August 2014 for one week. We've never been to Switzerland and are very excited! We're leaving the car at home and are planning to buy the Swiss Flexi Passes (2nd class). We're staying in Lauterbrunnen and will be flying from London to Geneva (back from Zurich). Our first day involves quite a lot of travelling as we're taking the train from Geneva to Lauterbrunnen via Visp (we've chosen this route as I've been told it's very scenic). We're familiar with very overcrowded trains in the UK and wondered how Swiss trains compare? Am I right in thinking that seat reservations can't be made on ordinary trains? If so, do you reckon that the six of us will manage to get seats? I realise that the trains are likely to be busy in August but I'm just wondering how busy they get!! NB We're not planning to take trips on any of the Panoramic/special trains - I realise you can make advance seat reservations for these. Any tips/advice would be gratefully received. Thank you. Susie

Arno - thank you for your prompt response. That's very reassuring about the seating - I know our children will be quite tired on that first day after an early flight from London. Your advice about travelling to Brig and then switching to a local train is also very helpful. Fantastic. I'm sure I'll have more questions over the coming months! Susie