Bicycling with small children

Check Blue Fox Travel which used to be Blue Bike. They have a private family tour in Paris.

A 4 year old should not bike outside a playground. Get a child seat for your bike.

We have rented in the Netherlands. I do not remember seeing child sized bikes or tandem attachment available for rent. BUT, we were not looking for that either so the bikes could have been in a corner and we would not have noticed them. And I do not recall seeing anyone using a tandem for a young child. A bike with training wheels would be impractical on the bike roads. The bike trails/roads in Europe are used heavily so a family clogging the road with training wheels and a tandem might be frown on so be courteous to the other users.

Also, the helmet culture as not wide spread in Europe so if helmets are important you need to bring your own.

Thanks for the replies. Here in America its pretty common to find a tandem or a trailer. I'll hope that those are available somewhere along the way. If I find any definitive info then I'll share the knowledge here.

check out www.crazyguyonabike.com
It has been several years since I biked the Loire, but I found there to be very little traffic on roads which are white on the Michelin 1:2000,000 maps

I have occasionally seen folks biking with young children in trailers, but I couldn't tell you in what countries or whether the bikers owned the equipment or had rented it. Have you tried doing some Googling? I'll bet there's information out there.

I'll add Beaune ...if you like wine especially. The wine trails have an occasional car/tractor or small town but are pretty easy and beautiful. bike rental
You can check out the local bike shop with family options. We can't wait to go back.
We also rode in Amsterdam and the trails North of the city were really easy, a guide would help make it easier for a family and I'm sure you can find any type of bike you want in Amsterdam.

Look at the list of types of bikes for hire on this site, and then click through to the Vendée link to contact a rep in the Pays de la Loire (or to any of the other areas that they cover). I know that the rep in the Charente Maritime area has a young family himself and I am confident he would give you good advice about options for children.

I rented a bike to tour the Loire valley. There is a specific bike route along the river there that is protected from traffic most of the time. Riding along the river was pretty easy and flat, there was some difficult peddling climbing up off the river at times. Towns like Amboise and some chateaux, like Villandry, were easy. Other towns, like Tours, had crazy traffic and no easy route through town (that I found). Chateaux like Chenonceau required a steep climb off the river before becoming reasonable rolling hills (about 22 km).

Tandem bikes were a rental choice but I didn't notice kids bikes. In Denmark and Netherlands I noticed a lot of bikes had three wheels with a cart in front to seat one or two small children. Most of the places I rode in France I'd feel comfortable with a 10 year old in the back of a tandem bike. I'm not sure a 4 year old would fit and I wouldn't feel comfortable with them riding alone. Ask the bike rental place for options, I'm sure they will have ideas. Without better French, on my part, I didn't feel I could rely on them for guidance on route choices.