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Covid19 Update: Our shop is open but you can still buy online for home delivery, or collection from our nearby sister shop on Fossgate. The lockdown is causing courier delays outside of our control. If you need your order urgently, please upgrade to Next Day Delivery, and please understand that we cannot guarantee any delivery times at the moment.

Harry Potter Kids T-Shirt - I Solemnly Swear

In stock


Sometimes your kids are little angels – and sometimes they act like Fred and George Weasley! Get them to declare their intentions for troublemaking straight up and let this I Solemnly Swear t-shirt do the talking for them. Black in colour, the quote, “I Solemnly Swear That I Am Up To No Good” is emblazoned on the front in white gothic script, with twin wands, scrollwork, and the Harry Potter logo. It’s the perfect piece of clothing for your little magical mischief-makers.

100% Cotton. Machine washable. Available in ages:

Age 3-4: Width 35cm (14 inches) x length 45cm (18 inches)

Age 5-6: Width 38cm (15 inches) x length 48cm (19 inches)

Age 7-8: Width 41cm (16 inches) x length 52cm (20 inches)

Age 9-11: Width 44cm (17 inches) x length 56cm (22 inches)

Age 12-14: Width 47cm (18.5 inches) x length 59cm (23 inches)

All measurements taken whilst garment is lying flat. Length is shoulder to hem, width is beneath the armpits.

To see the rest of our Harry Potter kids t-shirts visit the Apparel section of The Shop That Must Not Be Named website, which specialises in official Harry Potter merchandise and gifts.


Collection (in York)

If you would like to collect your order from our shop in York, select the 'Click & Collect' delivery option at checkout. Once your order has been picked we will contact you to let you know it is ready for you to pick up.

UK Delivery

Standard Delivery on orders under £40 costs £1.50* for Large Letters and £3.95* for Small-Medium Parcels. Delivery takes 3-5 working days.

Standard Delivery on orders over £40 is free* and takes 3-5 working days.

*Some of the bulky/heavy items we offer for sale are excluded from our standard delivery charges and may incur a postage surcharge. If applicable, this is mentioned in the item description. You will be made aware of this during the checkout process.

Next Day Delivery (UK Mainland ONLY) costs £6.95 for Large Letters and £9.95 for Small-Medium Parcels. Orders must be placed before 2pm, Monday to Friday only, excluding Bank Holidays. Next Day Delivery cannot be guaranteed on Saturdays. All Next Day orders placed on weekends will be delivered on Tuesday.

International Delivery

Delivery to Europe costs from £12.95**.

Delivery to the Rest of the World costs from £19.95**.

**It may sometimes be possible that the standard international delivery charges set out above will prove insufficient for especially bulky/heavy parcels. In this case we will contact you and offer you a postage surcharge to meet the cost of shipping your order. Should you not wish to pay this surcharge we will refund your payment in full and cancel your order. Similarly, some of the smaller and lighter items we sell may cost less to post in which case we will issue a partial postage refund once your order is on its way.

All international deliveries come with tracking and require a signature upon receipt.

Please be aware that receiving goods in countries other than European Union member states may incur import duties and/or local taxes which are your responsibility.

Gift Vouchers

You can purchase gift vouchers for The Shop That Must Not Be Named which can be spent both in store and on our website. Standard delivery for vouchers is free worldwide, unless you choose to upgrade your postage (for example, to Next Day Delivery) or if you purchase them with other items subject to a delivery charge.


  • No refunds/exchanges after 14 days of delivery.
  • Damaged Items: When good are received in a faulty condition, the customer is entitled to a replacement product, or a full money refund, including postage and return postage.
  • Buyer Remorse: If you have changed your mind about an item you bought, you are entitled to an exchange, or a full money refund, excluding postage and return postage.
  • What to do: To initiate a refund or exchange, please contact us. We will ask you to return the goods in their original condition, with their original packaging and tags. We always recommend using a recorded delivery service and keeping proof of postage, as we cannot be held responsible if returned items are lost in transit.
  • Please allow 14 days for returns to be processed.
  • We regret that due to hygiene regulations, unwanted earrings cannot be returned.

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