Children pick things up from the ground all the time especially bugs, worms and lizards. If a child puts a tick in his/her mouth, this could be concerning. If the tick has a tick disease then it could burst inside the child's mouth; and spread the infection including Lyme Disease. This could happen from a cold sore on the mouth or a scratch on the gums.
Kids that pick up ticks from the ground may have spotted them first in the grass; or perhaps the tick fell off a pet. However it happens, be sure to keep watch on kids; take them to the doctor for evaluation; and look out for signs of Lyme Disease.