Insurance specialists Call Wiser warned the rules around stickers on a car were not clear-cut and motorists should check before facing any implications.
In an online statement, Call Wiser said: “While a National Trust or “baby on board” sticker might seem innocuous, you should still raise the issue with your insurer to prevent ending up in hot water.”
Car insurance providers must be informed of any upgrades so they can alter your premiums and put you on the right price band.
Motorists cannot have their policy invalidated if the modifications have been pre-agreed by an insurance provider.
However, insurers all follow their own unique guidelines so new parents are urged to call their provider to see whether a sticker will make any difference to their cover.