If you think your 3yo will do it (ie, giving him a “big boy” responsibility) you could try having him go ahead of you with his arms crossed across his chest, to receive a blessing by the priest – this has been a big success with my little relatives.
On the other hand, if this doesn’t seem like it is going to be a good solution, by all means receive on the tongue. Receiving Holy Communion on the tongue is the universal norm for the Church – the United States had to get special permission to receive in the hand! Never be afraid or ashamed of receiving on the tongue, whether or not other people do it.
Caution - once one begins to receive on the tongue, chances are that you will never want to receive in the hand again!! (Besides feeling more appropriate in itself, you never have to worry about having crumbs on your hands again, or worry about whether you washed your hands, or worry about the germs you might have picked up during the sign of peace…)