Our children, 2 1/2 and 4 are welcome in our bed also.  But lately our 4
year old, who has been toilet trained for less than a year, has been
wetting our bed. Twice this week.

We've decided to introduce the mattress-on-the-floor approach.  His
mattress is next to our bed on the bedroom floor.  We've explained to him
that while we enjoy sleeping with HIM we do not enjoy sleeping with his
urine.  If he wakes up dry he is more than welcome to join us in the
morning for a nice cuddle, or a change of clothes and a cuddle.

The 2 1/2 year-old is playing the toilet training game, and going through
diapers like water (she takes them off every hour and insists on a new
one).

Good luck,

Nofia