There seems little point paying for a meal that a child may not eat, so speak to the venue and make sure that they can offer an alternative. At least you know the children will enjoy it and hopefully, it will keep the cost down as well!
There are so many options now for keeping children entertained during the day, from simple ideas like putting together an activity pack for them to employing a creche.
A mobile creche can cater for all ages and will ensure that all children are properly supervised as well as kept busy. Maybe as a treat, book a magician or a face painter to come along and allow the speeches to take place without any "heckling" from the younger guests!
Also, consider having a Creche service at your wedding.