Introduction
You will be able to continue with your crafts and hobbies while in the Netherlands but buying your bits & bobs will take a bit of hunting around the various stores to find what you want. There are no craft or sewing superstores here, but a fairly reasonable selection of smaller specialty stores. There are a many items that you will not find at either the craft, knitting, sewing or fabric stores but at the local markets.

Sewing - Sewing Machines, Fabrics & Notions
Sewing stores are generally split into Machine (Naaimachines) and Fabric (modestoffen or stoffenwinkel) stores. Machine stores both sell and service machines and stock a range of additional items including scissors, buttons, thread, zips, pins, cord etc. They are separate from fabric stores, which don't stock machines or provide machine services but do stock the bric-a-brac as well as fabric. Machine stores can be found in pretty much all shopping centres and several in the city centre of Rotterdam, fabric stores however are a little harder to find.
Fabric (Stoffen)
Schroder Stoffenhandel
Coolsingel 79, 3012AE, Rotterdam centrum
Naaimachines
There are 13 stores in the Rotterdam centre area, the stores stock a variety of models and makes of sewing machines and overlockers and sell a basic range of sewing notions, you can also have your machines serviced at these stores. You can search in Goudengids under 'Naaimachines' to get the full listing. Below is a selection:
Van Doorn Naaimachines
website - http://www.vandoornnaaimachines.nl
Meent 124, 3011JS, Rotterdam centrum
Matson Naaimachine Speciaalzaak
website - http://www.matson.nl
Matson have three stores in Rotterdam.
Klein Naaimachines
Kleiweg 103-B, 3051GL, Rotterdam

Crafts & hobbies
There are quite a few crafty stores around the Rotterdam region stocking a fairly good selection of all things craft. Pipoos seem to have the most stores and stock a basic range of scrapbooking supplies. You will find most of what you are looking for (including papers, stamps, dowels, beads, scissors, tapes, felts etc) in these stores.
Most of the craft stores sell polystyrene balls in varying sizes for making pomanders, decorating & craft projects, however they don't stock things like bulk bags of polystyrene beads for sewing projects like beanbags etc, neither do the sewing stores. For this sort of item and (anything upholstery related), you will have to shop at the markets around the city.
Breierij-Uniek
Benedenrywg 32, 2982XB, Ridderkerk
De Witte Arend Hobbywinkeltje
Schere 97, 3085DV, Rotterdam
Cijs and Groene wof
website - http://www.cijs-hobbyshop.nl
Kl Beer 3, 3067ZW, Rotterdam
Hannewijk Mohle Creatif
Voorschoterlaan 84, 3062KS, Rotterdam
Wim Bakker Kreative
Pannenkoekstraat 50a, 3011LH, Rotterdam centrum
Fluiterin 430, 2903HN, Capelle a/d Ijssel
Pipoos
website - http://www.pipoos.nl/winkeladres.php?Sort=13
Binnenwegplein 6c, 3012KA, Rotterdam centrum
Pipoos Zuidplein
Winkelcentrum Zuidplein
Zuidplein Hoog 970, 3083BS, Rotterdam Zuid
Knip-In Stoffen
Zwaanhals 572, 3035KT, Rotterdam
Fa. Cijs
Kleine beer 3, 3067ZW, Rotterdam
De Creatieve Lijn
Celesta 67, 3068HH, Rotterdam
Kantoorboekhandel Feyenoord
website - http://www.allesinrotterdam.nl/item/20/2035/ia2035_153846.html
Groenehilledijk 163, 3073AB, Rotterdam
Van Rietschoten Kantoorv
H. Keizerswaard 26, 3078AM, Rotterdam
Kralen & Kralen
Meerwedesingel 48, 2953TG, Barendrecht

Scrapbooking
Scrapbooking is still in fledgling stages in the Netherlands; there is only one dedicated shop in Rotterdam, they have another store in Hilversum, north of Amsterdam, their stock is limited and they do run workshops (in dutch). Some of the craft stores listed above sell a basic range of scrapbooking items also.
Pien's Atelier, Scrapbooking store
website - http://www.piensatelier.nl
Pannekoekstraat 72a-74a, 3011LK, Rotterdam centrum

Knitting, Needlepoint & handiwork
There are some lovely boutique stores catering to this part of the creative spectrum.
For knitting and needlepoint try:
Lialaine Wol en Handworkhuis
website - http://www.lydialaine.nl/
Goudesingel 231a, 3031EK, Rotterdam centrum
Has a great array of wool, needlepoint wool and cotton, printed canvases, framing, linen. They do not do have a stretching service for completed canvases.
Wolle Willy
Wolphaertsbocht 285, 3083MP, Rotterdam

Painting, drawing & design
Due to the large student population and the Hoogeschool Rotterdam, the art stores are very good and stock a comprehensive range of supplies.
Beek Art Supplies BV
website - http://www.vanbeekonline.com
Hoogstraat 58/64, 3011 PT, Rotterdam centrum
Harold’s Grafik
website - http://www.harolds.nl
Burg van Walsumweg 730, 3011MZ, Rotterdam centrum
A comprehensive supplier of fine arts supplies, canvas’s, satchels, books, easels etc

Beading
Costume jewelry is popular in the Netherlands so is jewelry making. You can buy beads and items you need to create you pieces from the craft stores mentioned above but there are also other avenues; online and speciality stores. You can take workshops at the various stores - specialist and general and there are also companies that will come to your home and host a jewelry making party.
Specialty stores
Heartbeads Bijoux
website - http://www.heart-beads.nl
Zeugstraat 32, 2801KE, Gouda
Pronkjuweel
website - http://www.pronk-juweel.nl
Pannekoekstraat 35a - 37a, 3011CC, Rotterdam centrum
Pronkjuweel do hold instore workshops for €40,00 per person, you can register and pay online.
Woopie
website - http://www.woopie-kralen.nl/index.php?page=home
Beneden Oostzeedijk 111-115, 3061VP, Rotterdam
Woopie also do workshops, children's parties and casual sessions with other jewelry makers.
Online stores
For a more comprehensive listing of all the online stores for beadwork and crafts go to this search page -
Pagina www.kralen.verzamelgids.nl/index.html
Beadifulsieraden
website - www.beadifulsieraden.nl
Beadles
website - www.beadles.nl
Beads & More
website - www.beadsandmore.tk
Karin's Bijoux
website - www.karinsbijoux.nl
Store in Rotterdam

Creating with recycled materials
Scrap
website - http://www.stichtingscrap.nl
Voorhaven 39, 3025HD, Delfshaven
A shop that is serious about recycling all sorts of things. You can purchase a huge variety of recycled products to create what ever you are interested in. Staff are on hand to advise and give ideas or help you in your search.