Your toothpaste tube is sealed under the cap for hygiene.
Remove the safety seal and then replace the flip-top cap.
During normal use, small amounts of crystallized toothpaste will build up on the mouth of the cap.
It's important to always keep your toothbrush clean, and sterilize the head regularly. When the toothbrush comes into contact with the opening of the toothpaste cap, bacteria etc. can be transferred to the tube.
Please don't allow children to suck on the toothpaste tube. We know it tastes yummy, but it's unhygienic (can spoil the toothpaste) and not the intended use for Jack N' Jill. If this does occur then immediately clean the tube as above.