Rooms normally aren't assigned to guests until you arrive at the front desk.
Two suggestions:
If your room is ready when you arrive, have someone distract the kids while you run ahead and plant the stuff.
If your room isn't ready, give the baskets to Bell Services along with your luggage and make arrangements to have the stuff delivered to the room when the room is ready. That will cost you a few bucks (tip) and you'll have to make sure to stay away from the hotel long enough to get the job done.